<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width"> <meta name="nodejs.org:node-version" content="v16.20.0"> <title>Util | Node.js v16.20.0 Documentation</title> <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Lato:400,700,400italic&display=fallback"> <link rel="stylesheet" href="assets/style.css"> <link rel="stylesheet" href="assets/hljs.css"> <link rel="canonical" href="https://nodejs.org/api/util.html"> <script async defer src="assets/api.js" type="text/javascript"></script> <style>@media(max-width:566px){.with-43-chars>.js-flavor-selector{float:none;margin:0 0 1em auto;}}</style> </head> <body class="alt apidoc" id="api-section-util"> <div id="content" class="clearfix"> <div id="column2" class="interior"> <div id="intro" class="interior"> <a href="/" title="Go back to the home page"> Node.js </a> </div> <ul> <li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> <li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> </ul> <hr class="line"> <ul> <li><a href="assert.html" class="nav-assert">Assertion testing</a></li> <li><a href="async_context.html" class="nav-async_context">Asynchronous context tracking</a></li> <li><a href="async_hooks.html" class="nav-async_hooks">Async hooks</a></li> <li><a href="buffer.html" class="nav-buffer">Buffer</a></li> <li><a href="addons.html" class="nav-addons">C++ addons</a></li> <li><a href="n-api.html" class="nav-n-api">C/C++ addons with Node-API</a></li> <li><a href="embedding.html" class="nav-embedding">C++ embedder API</a></li> <li><a href="child_process.html" class="nav-child_process">Child processes</a></li> <li><a href="cluster.html" class="nav-cluster">Cluster</a></li> <li><a href="cli.html" class="nav-cli">Command-line options</a></li> <li><a href="console.html" class="nav-console">Console</a></li> <li><a href="corepack.html" class="nav-corepack">Corepack</a></li> <li><a href="crypto.html" class="nav-crypto">Crypto</a></li> <li><a href="debugger.html" class="nav-debugger">Debugger</a></li> <li><a href="deprecations.html" class="nav-deprecations">Deprecated APIs</a></li> <li><a href="diagnostics_channel.html" class="nav-diagnostics_channel">Diagnostics Channel</a></li> <li><a href="dns.html" class="nav-dns">DNS</a></li> <li><a href="domain.html" class="nav-domain">Domain</a></li> <li><a href="errors.html" class="nav-errors">Errors</a></li> <li><a href="events.html" class="nav-events">Events</a></li> <li><a href="fs.html" class="nav-fs">File system</a></li> <li><a href="globals.html" class="nav-globals">Globals</a></li> <li><a href="http.html" class="nav-http">HTTP</a></li> <li><a href="http2.html" class="nav-http2">HTTP/2</a></li> <li><a href="https.html" class="nav-https">HTTPS</a></li> <li><a href="inspector.html" class="nav-inspector">Inspector</a></li> <li><a href="intl.html" class="nav-intl">Internationalization</a></li> <li><a href="modules.html" class="nav-modules">Modules: CommonJS modules</a></li> <li><a href="esm.html" class="nav-esm">Modules: ECMAScript modules</a></li> <li><a href="module.html" class="nav-module">Modules: <code>node:module</code> API</a></li> <li><a href="packages.html" class="nav-packages">Modules: Packages</a></li> <li><a href="net.html" class="nav-net">Net</a></li> <li><a href="os.html" class="nav-os">OS</a></li> <li><a href="path.html" class="nav-path">Path</a></li> <li><a href="perf_hooks.html" class="nav-perf_hooks">Performance hooks</a></li> <li><a href="permissions.html" class="nav-permissions">Permissions</a></li> <li><a href="process.html" class="nav-process">Process</a></li> <li><a href="punycode.html" class="nav-punycode">Punycode</a></li> <li><a href="querystring.html" class="nav-querystring">Query strings</a></li> <li><a href="readline.html" class="nav-readline">Readline</a></li> <li><a href="repl.html" class="nav-repl">REPL</a></li> <li><a href="report.html" class="nav-report">Report</a></li> <li><a href="stream.html" class="nav-stream">Stream</a></li> <li><a href="string_decoder.html" class="nav-string_decoder">String decoder</a></li> <li><a href="test.html" class="nav-test">Test runner</a></li> <li><a href="timers.html" class="nav-timers">Timers</a></li> <li><a href="tls.html" class="nav-tls">TLS/SSL</a></li> <li><a href="tracing.html" class="nav-tracing">Trace events</a></li> <li><a href="tty.html" class="nav-tty">TTY</a></li> <li><a href="dgram.html" class="nav-dgram">UDP/datagram</a></li> <li><a href="url.html" class="nav-url">URL</a></li> <li><a href="util.html" class="nav-util active">Utilities</a></li> <li><a href="v8.html" class="nav-v8">V8</a></li> <li><a href="vm.html" class="nav-vm">VM</a></li> <li><a href="wasi.html" class="nav-wasi">WASI</a></li> <li><a href="webcrypto.html" class="nav-webcrypto">Web Crypto API</a></li> <li><a href="webstreams.html" class="nav-webstreams">Web Streams API</a></li> <li><a href="worker_threads.html" class="nav-worker_threads">Worker threads</a></li> <li><a href="zlib.html" class="nav-zlib">Zlib</a></li> </ul> <hr class="line"> <ul> <li><a href="https://github.com/nodejs/node" class="nav-https-github-com-nodejs-node">Code repository and issue tracker</a></li> </ul> </div> <div id="column1" data-id="util" class="interior"> <header class="header"> <div class="header-container"> <h1>Node.js v16.20.0 documentation</h1> <button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" aria-label="Toggle dark mode/light mode" hidden> <svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24"> <path fill="none" d="M0 0h24v24H0z" /> <path d="M11.1 12.08c-2.33-4.51-.5-8.48.53-10.07C6.27 2.2 1.98 6.59 1.98 12c0 .14.02.28.02.42.62-.27 1.29-.42 2-.42 1.66 0 3.18.83 4.1 2.15A4.01 4.01 0 0111 18c0 1.52-.87 2.83-2.12 3.51.98.32 2.03.5 3.11.5 3.5 0 6.58-1.8 8.37-4.52-2.36.23-6.98-.97-9.26-5.41z"/> <path d="M7 16h-.18C6.4 14.84 5.3 14 4 14c-1.66 0-3 1.34-3 3s1.34 3 3 3h3c1.1 0 2-.9 2-2s-.9-2-2-2z"/> </svg> <svg xmlns="http://www.w3.org/2000/svg" class="icon light-icon" height="24" width="24"> <path d="M0 0h24v24H0z" fill="none" /> <path d="M6.76 4.84l-1.8-1.79-1.41 1.41 1.79 1.79 1.42-1.41zM4 10.5H1v2h3v-2zm9-9.95h-2V3.5h2V.55zm7.45 3.91l-1.41-1.41-1.79 1.79 1.41 1.41 1.79-1.79zm-3.21 13.7l1.79 1.8 1.41-1.41-1.8-1.79-1.4 1.4zM20 10.5v2h3v-2h-3zm-8-5c-3.31 0-6 2.69-6 6s2.69 6 6 6 6-2.69 6-6-2.69-6-6-6zm-1 16.95h2V19.5h-2v2.95zm-7.45-3.91l1.41 1.41 1.79-1.8-1.41-1.41-1.79 1.8z"/> </svg> </button> </div> <div id="gtoc"> <ul> <li class="pinned-header">Node.js v16.20.0</li> <li class="picker-header"> <a href="#"> <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> Table of contents </a> <div class="picker"><div class="toc"><ul> <li><span class="stability_2"><a href="#util">Util</a></span> <ul> <li><a href="#utilcallbackifyoriginal"><code>util.callbackify(original)</code></a></li> <li><a href="#utildebuglogsection-callback"><code>util.debuglog(section[, callback])</code></a> <ul> <li><a href="#debuglogenabled"><code>debuglog().enabled</code></a></li> </ul> </li> <li><a href="#utildebugsection"><code>util.debug(section)</code></a></li> <li><a href="#utildeprecatefn-msg-code"><code>util.deprecate(fn, msg[, code])</code></a></li> <li><a href="#utilformatformat-args"><code>util.format(format[, ...args])</code></a></li> <li><a href="#utilformatwithoptionsinspectoptions-format-args"><code>util.formatWithOptions(inspectOptions, format[, ...args])</code></a></li> <li><a href="#utilgetsystemerrornameerr"><code>util.getSystemErrorName(err)</code></a></li> <li><a href="#utilgetsystemerrormap"><code>util.getSystemErrorMap()</code></a></li> <li><span class="stability_3"><a href="#utilinheritsconstructor-superconstructor"><code>util.inherits(constructor, superConstructor)</code></a></span></li> <li><a href="#utilinspectobject-options"><code>util.inspect(object[, options])</code></a></li> <li><a href="#utilinspectobject-showhidden-depth-colors"><code>util.inspect(object[, showHidden[, depth[, colors]]])</code></a> <ul> <li><a href="#customizing-utilinspect-colors">Customizing <code>util.inspect</code> colors</a> <ul> <li><a href="#modifiers">Modifiers</a></li> <li><a href="#foreground-colors">Foreground colors</a></li> <li><a href="#background-colors">Background colors</a></li> </ul> </li> <li><a href="#custom-inspection-functions-on-objects">Custom inspection functions on objects</a></li> <li><a href="#utilinspectcustom"><code>util.inspect.custom</code></a></li> <li><a href="#utilinspectdefaultoptions"><code>util.inspect.defaultOptions</code></a></li> </ul> </li> <li><a href="#utilisdeepstrictequalval1-val2"><code>util.isDeepStrictEqual(val1, val2)</code></a></li> <li><span class="stability_1"><a href="#utilparseargsconfig"><code>util.parseArgs([config])</code></a></span> <ul> <li><a href="#parseargs-tokens"><code>parseArgs</code> <code>tokens</code></a></li> </ul> </li> <li><a href="#utilpromisifyoriginal"><code>util.promisify(original)</code></a> <ul> <li><a href="#custom-promisified-functions">Custom promisified functions</a></li> <li><a href="#utilpromisifycustom"><code>util.promisify.custom</code></a></li> </ul> </li> <li><a href="#utilstripvtcontrolcharactersstr"><code>util.stripVTControlCharacters(str)</code></a></li> <li><a href="#class-utiltextdecoder">Class: <code>util.TextDecoder</code></a> <ul> <li><a href="#whatwg-supported-encodings">WHATWG supported encodings</a> <ul> <li><a href="#encodings-supported-by-default-with-full-icu-data">Encodings supported by default (with full ICU data)</a></li> <li><a href="#encodings-supported-when-nodejs-is-built-with-the-small-icu-option">Encodings supported when Node.js is built with the <code>small-icu</code> option</a></li> <li><a href="#encodings-supported-when-icu-is-disabled">Encodings supported when ICU is disabled</a></li> </ul> </li> <li><a href="#new-textdecoderencoding-options"><code>new TextDecoder([encoding[, options]])</code></a></li> <li><a href="#textdecoderdecodeinput-options"><code>textDecoder.decode([input[, options]])</code></a></li> <li><a href="#textdecoderencoding"><code>textDecoder.encoding</code></a></li> <li><a href="#textdecoderfatal"><code>textDecoder.fatal</code></a></li> <li><a href="#textdecoderignorebom"><code>textDecoder.ignoreBOM</code></a></li> </ul> </li> <li><a href="#class-utiltextencoder">Class: <code>util.TextEncoder</code></a> <ul> <li><a href="#textencoderencodeinput"><code>textEncoder.encode([input])</code></a></li> <li><a href="#textencoderencodeintosrc-dest"><code>textEncoder.encodeInto(src, dest)</code></a></li> <li><a href="#textencoderencoding"><code>textEncoder.encoding</code></a></li> </ul> </li> <li><a href="#utiltousvstringstring"><code>util.toUSVString(string)</code></a></li> <li><a href="#utiltypes"><code>util.types</code></a> <ul> <li><a href="#utiltypesisanyarraybuffervalue"><code>util.types.isAnyArrayBuffer(value)</code></a></li> <li><a href="#utiltypesisarraybufferviewvalue"><code>util.types.isArrayBufferView(value)</code></a></li> <li><a href="#utiltypesisargumentsobjectvalue"><code>util.types.isArgumentsObject(value)</code></a></li> <li><a href="#utiltypesisarraybuffervalue"><code>util.types.isArrayBuffer(value)</code></a></li> <li><a href="#utiltypesisasyncfunctionvalue"><code>util.types.isAsyncFunction(value)</code></a></li> <li><a href="#utiltypesisbigint64arrayvalue"><code>util.types.isBigInt64Array(value)</code></a></li> <li><a href="#utiltypesisbiguint64arrayvalue"><code>util.types.isBigUint64Array(value)</code></a></li> <li><a href="#utiltypesisbooleanobjectvalue"><code>util.types.isBooleanObject(value)</code></a></li> <li><a href="#utiltypesisboxedprimitivevalue"><code>util.types.isBoxedPrimitive(value)</code></a></li> <li><a href="#utiltypesiscryptokeyvalue"><code>util.types.isCryptoKey(value)</code></a></li> <li><a href="#utiltypesisdataviewvalue"><code>util.types.isDataView(value)</code></a></li> <li><a href="#utiltypesisdatevalue"><code>util.types.isDate(value)</code></a></li> <li><a href="#utiltypesisexternalvalue"><code>util.types.isExternal(value)</code></a></li> <li><a href="#utiltypesisfloat32arrayvalue"><code>util.types.isFloat32Array(value)</code></a></li> <li><a href="#utiltypesisfloat64arrayvalue"><code>util.types.isFloat64Array(value)</code></a></li> <li><a href="#utiltypesisgeneratorfunctionvalue"><code>util.types.isGeneratorFunction(value)</code></a></li> <li><a href="#utiltypesisgeneratorobjectvalue"><code>util.types.isGeneratorObject(value)</code></a></li> <li><a href="#utiltypesisint8arrayvalue"><code>util.types.isInt8Array(value)</code></a></li> <li><a href="#utiltypesisint16arrayvalue"><code>util.types.isInt16Array(value)</code></a></li> <li><a href="#utiltypesisint32arrayvalue"><code>util.types.isInt32Array(value)</code></a></li> <li><a href="#utiltypesiskeyobjectvalue"><code>util.types.isKeyObject(value)</code></a></li> <li><a href="#utiltypesismapvalue"><code>util.types.isMap(value)</code></a></li> <li><a href="#utiltypesismapiteratorvalue"><code>util.types.isMapIterator(value)</code></a></li> <li><a href="#utiltypesismodulenamespaceobjectvalue"><code>util.types.isModuleNamespaceObject(value)</code></a></li> <li><a href="#utiltypesisnativeerrorvalue"><code>util.types.isNativeError(value)</code></a></li> <li><a href="#utiltypesisnumberobjectvalue"><code>util.types.isNumberObject(value)</code></a></li> <li><a href="#utiltypesispromisevalue"><code>util.types.isPromise(value)</code></a></li> <li><a href="#utiltypesisproxyvalue"><code>util.types.isProxy(value)</code></a></li> <li><a href="#utiltypesisregexpvalue"><code>util.types.isRegExp(value)</code></a></li> <li><a href="#utiltypesissetvalue"><code>util.types.isSet(value)</code></a></li> <li><a href="#utiltypesissetiteratorvalue"><code>util.types.isSetIterator(value)</code></a></li> <li><a href="#utiltypesissharedarraybuffervalue"><code>util.types.isSharedArrayBuffer(value)</code></a></li> <li><a href="#utiltypesisstringobjectvalue"><code>util.types.isStringObject(value)</code></a></li> <li><a href="#utiltypesissymbolobjectvalue"><code>util.types.isSymbolObject(value)</code></a></li> <li><a href="#utiltypesistypedarrayvalue"><code>util.types.isTypedArray(value)</code></a></li> <li><a href="#utiltypesisuint8arrayvalue"><code>util.types.isUint8Array(value)</code></a></li> <li><a href="#utiltypesisuint8clampedarrayvalue"><code>util.types.isUint8ClampedArray(value)</code></a></li> <li><a href="#utiltypesisuint16arrayvalue"><code>util.types.isUint16Array(value)</code></a></li> <li><a href="#utiltypesisuint32arrayvalue"><code>util.types.isUint32Array(value)</code></a></li> <li><a href="#utiltypesisweakmapvalue"><code>util.types.isWeakMap(value)</code></a></li> <li><a href="#utiltypesisweaksetvalue"><code>util.types.isWeakSet(value)</code></a></li> <li><span class="stability_0"><a href="#utiltypesiswebassemblycompiledmodulevalue"><code>util.types.isWebAssemblyCompiledModule(value)</code></a></span></li> </ul> </li> <li><a href="#deprecated-apis">Deprecated APIs</a> <ul> <li><span class="stability_0"><a href="#util_extendtarget-source"><code>util._extend(target, source)</code></a></span></li> <li><span class="stability_0"><a href="#utilisarrayobject"><code>util.isArray(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisbooleanobject"><code>util.isBoolean(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisbufferobject"><code>util.isBuffer(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisdateobject"><code>util.isDate(object)</code></a></span></li> <li><span class="stability_0"><a href="#utiliserrorobject"><code>util.isError(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisfunctionobject"><code>util.isFunction(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisnullobject"><code>util.isNull(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisnullorundefinedobject"><code>util.isNullOrUndefined(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisnumberobject"><code>util.isNumber(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisobjectobject"><code>util.isObject(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisprimitiveobject"><code>util.isPrimitive(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisregexpobject"><code>util.isRegExp(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisstringobject"><code>util.isString(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilissymbolobject"><code>util.isSymbol(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisundefinedobject"><code>util.isUndefined(object)</code></a></span></li> <li><span class="stability_0"><a href="#utillogstring"><code>util.log(string)</code></a></span></li> </ul> </li> </ul> </li> </ul></div></div> </li> <li class="picker-header"> <a href="#"> <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> Index </a> <div class="picker"><ul> <li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> <li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> <li> <a href="index.html">Index</a> </li> </ul> <hr class="line"> <ul> <li><a href="assert.html" class="nav-assert">Assertion testing</a></li> <li><a href="async_context.html" class="nav-async_context">Asynchronous context tracking</a></li> <li><a href="async_hooks.html" class="nav-async_hooks">Async hooks</a></li> <li><a href="buffer.html" class="nav-buffer">Buffer</a></li> <li><a href="addons.html" class="nav-addons">C++ addons</a></li> <li><a href="n-api.html" class="nav-n-api">C/C++ addons with Node-API</a></li> <li><a href="embedding.html" class="nav-embedding">C++ embedder API</a></li> <li><a href="child_process.html" class="nav-child_process">Child processes</a></li> <li><a href="cluster.html" class="nav-cluster">Cluster</a></li> <li><a href="cli.html" class="nav-cli">Command-line options</a></li> <li><a href="console.html" class="nav-console">Console</a></li> <li><a href="corepack.html" class="nav-corepack">Corepack</a></li> <li><a href="crypto.html" class="nav-crypto">Crypto</a></li> <li><a href="debugger.html" class="nav-debugger">Debugger</a></li> <li><a href="deprecations.html" class="nav-deprecations">Deprecated APIs</a></li> <li><a href="diagnostics_channel.html" class="nav-diagnostics_channel">Diagnostics Channel</a></li> <li><a href="dns.html" class="nav-dns">DNS</a></li> <li><a href="domain.html" class="nav-domain">Domain</a></li> <li><a href="errors.html" class="nav-errors">Errors</a></li> <li><a href="events.html" class="nav-events">Events</a></li> <li><a href="fs.html" class="nav-fs">File system</a></li> <li><a href="globals.html" class="nav-globals">Globals</a></li> <li><a href="http.html" class="nav-http">HTTP</a></li> <li><a href="http2.html" class="nav-http2">HTTP/2</a></li> <li><a href="https.html" class="nav-https">HTTPS</a></li> <li><a href="inspector.html" class="nav-inspector">Inspector</a></li> <li><a href="intl.html" class="nav-intl">Internationalization</a></li> <li><a href="modules.html" class="nav-modules">Modules: CommonJS modules</a></li> <li><a href="esm.html" class="nav-esm">Modules: ECMAScript modules</a></li> <li><a href="module.html" class="nav-module">Modules: <code>node:module</code> API</a></li> <li><a href="packages.html" class="nav-packages">Modules: Packages</a></li> <li><a href="net.html" class="nav-net">Net</a></li> <li><a href="os.html" class="nav-os">OS</a></li> <li><a href="path.html" class="nav-path">Path</a></li> <li><a href="perf_hooks.html" class="nav-perf_hooks">Performance hooks</a></li> <li><a href="permissions.html" class="nav-permissions">Permissions</a></li> <li><a href="process.html" class="nav-process">Process</a></li> <li><a href="punycode.html" class="nav-punycode">Punycode</a></li> <li><a href="querystring.html" class="nav-querystring">Query strings</a></li> <li><a href="readline.html" class="nav-readline">Readline</a></li> <li><a href="repl.html" class="nav-repl">REPL</a></li> <li><a href="report.html" class="nav-report">Report</a></li> <li><a href="stream.html" class="nav-stream">Stream</a></li> <li><a href="string_decoder.html" class="nav-string_decoder">String decoder</a></li> <li><a href="test.html" class="nav-test">Test runner</a></li> <li><a href="timers.html" class="nav-timers">Timers</a></li> <li><a href="tls.html" class="nav-tls">TLS/SSL</a></li> <li><a href="tracing.html" class="nav-tracing">Trace events</a></li> <li><a href="tty.html" class="nav-tty">TTY</a></li> <li><a href="dgram.html" class="nav-dgram">UDP/datagram</a></li> <li><a href="url.html" class="nav-url">URL</a></li> <li><a href="util.html" class="nav-util active">Utilities</a></li> <li><a href="v8.html" class="nav-v8">V8</a></li> <li><a href="vm.html" class="nav-vm">VM</a></li> <li><a href="wasi.html" class="nav-wasi">WASI</a></li> <li><a href="webcrypto.html" class="nav-webcrypto">Web Crypto API</a></li> <li><a href="webstreams.html" class="nav-webstreams">Web Streams API</a></li> <li><a href="worker_threads.html" class="nav-worker_threads">Worker threads</a></li> <li><a href="zlib.html" class="nav-zlib">Zlib</a></li> </ul> <hr class="line"> <ul> <li><a href="https://github.com/nodejs/node" class="nav-https-github-com-nodejs-node">Code repository and issue tracker</a></li> </ul></div> </li> <li class="picker-header"> <a href="#"> <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> Other versions </a> <div class="picker"><ol id="alt-docs"><li><a href="https://nodejs.org/docs/latest-v19.x/api/util.html">19.x</a></li> <li><a href="https://nodejs.org/docs/latest-v18.x/api/util.html">18.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v17.x/api/util.html">17.x</a></li> <li><a href="https://nodejs.org/docs/latest-v16.x/api/util.html">16.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v15.x/api/util.html">15.x</a></li> <li><a href="https://nodejs.org/docs/latest-v14.x/api/util.html">14.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v13.x/api/util.html">13.x</a></li> <li><a href="https://nodejs.org/docs/latest-v12.x/api/util.html">12.x</a></li> <li><a href="https://nodejs.org/docs/latest-v11.x/api/util.html">11.x</a></li> <li><a href="https://nodejs.org/docs/latest-v10.x/api/util.html">10.x</a></li> <li><a href="https://nodejs.org/docs/latest-v9.x/api/util.html">9.x</a></li> <li><a href="https://nodejs.org/docs/latest-v8.x/api/util.html">8.x</a></li> <li><a href="https://nodejs.org/docs/latest-v7.x/api/util.html">7.x</a></li> <li><a href="https://nodejs.org/docs/latest-v6.x/api/util.html">6.x</a></li> <li><a href="https://nodejs.org/docs/latest-v5.x/api/util.html">5.x</a></li> <li><a href="https://nodejs.org/docs/latest-v4.x/api/util.html">4.x</a></li> <li><a href="https://nodejs.org/docs/latest-v0.12.x/api/util.html">0.12.x</a></li> <li><a href="https://nodejs.org/docs/latest-v0.10.x/api/util.html">0.10.x</a></li></ol></div> </li> <li class="picker-header"> <a href="#"> <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> Options </a> <div class="picker"> <ul> <li> <a href="all.html">View on single page</a> </li> <li> <a href="util.json">View as JSON</a> </li> <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/util.md">Edit on GitHub</a></li> </ul> </div> </li> </ul> </div> <hr> </header> <details id="toc" open><summary>Table of contents</summary><ul> <li><span class="stability_2"><a href="#util">Util</a></span> <ul> <li><a href="#utilcallbackifyoriginal"><code>util.callbackify(original)</code></a></li> <li><a href="#utildebuglogsection-callback"><code>util.debuglog(section[, callback])</code></a> <ul> <li><a href="#debuglogenabled"><code>debuglog().enabled</code></a></li> </ul> </li> <li><a href="#utildebugsection"><code>util.debug(section)</code></a></li> <li><a href="#utildeprecatefn-msg-code"><code>util.deprecate(fn, msg[, code])</code></a></li> <li><a href="#utilformatformat-args"><code>util.format(format[, ...args])</code></a></li> <li><a href="#utilformatwithoptionsinspectoptions-format-args"><code>util.formatWithOptions(inspectOptions, format[, ...args])</code></a></li> <li><a href="#utilgetsystemerrornameerr"><code>util.getSystemErrorName(err)</code></a></li> <li><a href="#utilgetsystemerrormap"><code>util.getSystemErrorMap()</code></a></li> <li><span class="stability_3"><a href="#utilinheritsconstructor-superconstructor"><code>util.inherits(constructor, superConstructor)</code></a></span></li> <li><a href="#utilinspectobject-options"><code>util.inspect(object[, options])</code></a></li> <li><a href="#utilinspectobject-showhidden-depth-colors"><code>util.inspect(object[, showHidden[, depth[, colors]]])</code></a> <ul> <li><a href="#customizing-utilinspect-colors">Customizing <code>util.inspect</code> colors</a> <ul> <li><a href="#modifiers">Modifiers</a></li> <li><a href="#foreground-colors">Foreground colors</a></li> <li><a href="#background-colors">Background colors</a></li> </ul> </li> <li><a href="#custom-inspection-functions-on-objects">Custom inspection functions on objects</a></li> <li><a href="#utilinspectcustom"><code>util.inspect.custom</code></a></li> <li><a href="#utilinspectdefaultoptions"><code>util.inspect.defaultOptions</code></a></li> </ul> </li> <li><a href="#utilisdeepstrictequalval1-val2"><code>util.isDeepStrictEqual(val1, val2)</code></a></li> <li><span class="stability_1"><a href="#utilparseargsconfig"><code>util.parseArgs([config])</code></a></span> <ul> <li><a href="#parseargs-tokens"><code>parseArgs</code> <code>tokens</code></a></li> </ul> </li> <li><a href="#utilpromisifyoriginal"><code>util.promisify(original)</code></a> <ul> <li><a href="#custom-promisified-functions">Custom promisified functions</a></li> <li><a href="#utilpromisifycustom"><code>util.promisify.custom</code></a></li> </ul> </li> <li><a href="#utilstripvtcontrolcharactersstr"><code>util.stripVTControlCharacters(str)</code></a></li> <li><a href="#class-utiltextdecoder">Class: <code>util.TextDecoder</code></a> <ul> <li><a href="#whatwg-supported-encodings">WHATWG supported encodings</a> <ul> <li><a href="#encodings-supported-by-default-with-full-icu-data">Encodings supported by default (with full ICU data)</a></li> <li><a href="#encodings-supported-when-nodejs-is-built-with-the-small-icu-option">Encodings supported when Node.js is built with the <code>small-icu</code> option</a></li> <li><a href="#encodings-supported-when-icu-is-disabled">Encodings supported when ICU is disabled</a></li> </ul> </li> <li><a href="#new-textdecoderencoding-options"><code>new TextDecoder([encoding[, options]])</code></a></li> <li><a href="#textdecoderdecodeinput-options"><code>textDecoder.decode([input[, options]])</code></a></li> <li><a href="#textdecoderencoding"><code>textDecoder.encoding</code></a></li> <li><a href="#textdecoderfatal"><code>textDecoder.fatal</code></a></li> <li><a href="#textdecoderignorebom"><code>textDecoder.ignoreBOM</code></a></li> </ul> </li> <li><a href="#class-utiltextencoder">Class: <code>util.TextEncoder</code></a> <ul> <li><a href="#textencoderencodeinput"><code>textEncoder.encode([input])</code></a></li> <li><a href="#textencoderencodeintosrc-dest"><code>textEncoder.encodeInto(src, dest)</code></a></li> <li><a href="#textencoderencoding"><code>textEncoder.encoding</code></a></li> </ul> </li> <li><a href="#utiltousvstringstring"><code>util.toUSVString(string)</code></a></li> <li><a href="#utiltypes"><code>util.types</code></a> <ul> <li><a href="#utiltypesisanyarraybuffervalue"><code>util.types.isAnyArrayBuffer(value)</code></a></li> <li><a href="#utiltypesisarraybufferviewvalue"><code>util.types.isArrayBufferView(value)</code></a></li> <li><a href="#utiltypesisargumentsobjectvalue"><code>util.types.isArgumentsObject(value)</code></a></li> <li><a href="#utiltypesisarraybuffervalue"><code>util.types.isArrayBuffer(value)</code></a></li> <li><a href="#utiltypesisasyncfunctionvalue"><code>util.types.isAsyncFunction(value)</code></a></li> <li><a href="#utiltypesisbigint64arrayvalue"><code>util.types.isBigInt64Array(value)</code></a></li> <li><a href="#utiltypesisbiguint64arrayvalue"><code>util.types.isBigUint64Array(value)</code></a></li> <li><a href="#utiltypesisbooleanobjectvalue"><code>util.types.isBooleanObject(value)</code></a></li> <li><a href="#utiltypesisboxedprimitivevalue"><code>util.types.isBoxedPrimitive(value)</code></a></li> <li><a href="#utiltypesiscryptokeyvalue"><code>util.types.isCryptoKey(value)</code></a></li> <li><a href="#utiltypesisdataviewvalue"><code>util.types.isDataView(value)</code></a></li> <li><a href="#utiltypesisdatevalue"><code>util.types.isDate(value)</code></a></li> <li><a href="#utiltypesisexternalvalue"><code>util.types.isExternal(value)</code></a></li> <li><a href="#utiltypesisfloat32arrayvalue"><code>util.types.isFloat32Array(value)</code></a></li> <li><a href="#utiltypesisfloat64arrayvalue"><code>util.types.isFloat64Array(value)</code></a></li> <li><a href="#utiltypesisgeneratorfunctionvalue"><code>util.types.isGeneratorFunction(value)</code></a></li> <li><a href="#utiltypesisgeneratorobjectvalue"><code>util.types.isGeneratorObject(value)</code></a></li> <li><a href="#utiltypesisint8arrayvalue"><code>util.types.isInt8Array(value)</code></a></li> <li><a href="#utiltypesisint16arrayvalue"><code>util.types.isInt16Array(value)</code></a></li> <li><a href="#utiltypesisint32arrayvalue"><code>util.types.isInt32Array(value)</code></a></li> <li><a href="#utiltypesiskeyobjectvalue"><code>util.types.isKeyObject(value)</code></a></li> <li><a href="#utiltypesismapvalue"><code>util.types.isMap(value)</code></a></li> <li><a href="#utiltypesismapiteratorvalue"><code>util.types.isMapIterator(value)</code></a></li> <li><a href="#utiltypesismodulenamespaceobjectvalue"><code>util.types.isModuleNamespaceObject(value)</code></a></li> <li><a href="#utiltypesisnativeerrorvalue"><code>util.types.isNativeError(value)</code></a></li> <li><a href="#utiltypesisnumberobjectvalue"><code>util.types.isNumberObject(value)</code></a></li> <li><a href="#utiltypesispromisevalue"><code>util.types.isPromise(value)</code></a></li> <li><a href="#utiltypesisproxyvalue"><code>util.types.isProxy(value)</code></a></li> <li><a href="#utiltypesisregexpvalue"><code>util.types.isRegExp(value)</code></a></li> <li><a href="#utiltypesissetvalue"><code>util.types.isSet(value)</code></a></li> <li><a href="#utiltypesissetiteratorvalue"><code>util.types.isSetIterator(value)</code></a></li> <li><a href="#utiltypesissharedarraybuffervalue"><code>util.types.isSharedArrayBuffer(value)</code></a></li> <li><a href="#utiltypesisstringobjectvalue"><code>util.types.isStringObject(value)</code></a></li> <li><a href="#utiltypesissymbolobjectvalue"><code>util.types.isSymbolObject(value)</code></a></li> <li><a href="#utiltypesistypedarrayvalue"><code>util.types.isTypedArray(value)</code></a></li> <li><a href="#utiltypesisuint8arrayvalue"><code>util.types.isUint8Array(value)</code></a></li> <li><a href="#utiltypesisuint8clampedarrayvalue"><code>util.types.isUint8ClampedArray(value)</code></a></li> <li><a href="#utiltypesisuint16arrayvalue"><code>util.types.isUint16Array(value)</code></a></li> <li><a href="#utiltypesisuint32arrayvalue"><code>util.types.isUint32Array(value)</code></a></li> <li><a href="#utiltypesisweakmapvalue"><code>util.types.isWeakMap(value)</code></a></li> <li><a href="#utiltypesisweaksetvalue"><code>util.types.isWeakSet(value)</code></a></li> <li><span class="stability_0"><a href="#utiltypesiswebassemblycompiledmodulevalue"><code>util.types.isWebAssemblyCompiledModule(value)</code></a></span></li> </ul> </li> <li><a href="#deprecated-apis">Deprecated APIs</a> <ul> <li><span class="stability_0"><a href="#util_extendtarget-source"><code>util._extend(target, source)</code></a></span></li> <li><span class="stability_0"><a href="#utilisarrayobject"><code>util.isArray(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisbooleanobject"><code>util.isBoolean(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisbufferobject"><code>util.isBuffer(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisdateobject"><code>util.isDate(object)</code></a></span></li> <li><span class="stability_0"><a href="#utiliserrorobject"><code>util.isError(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisfunctionobject"><code>util.isFunction(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisnullobject"><code>util.isNull(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisnullorundefinedobject"><code>util.isNullOrUndefined(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisnumberobject"><code>util.isNumber(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisobjectobject"><code>util.isObject(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisprimitiveobject"><code>util.isPrimitive(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisregexpobject"><code>util.isRegExp(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisstringobject"><code>util.isString(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilissymbolobject"><code>util.isSymbol(object)</code></a></span></li> <li><span class="stability_0"><a href="#utilisundefinedobject"><code>util.isUndefined(object)</code></a></span></li> <li><span class="stability_0"><a href="#utillogstring"><code>util.log(string)</code></a></span></li> </ul> </li> </ul> </li> </ul></details> <div id="apicontent"> <h2>Util<span><a class="mark" href="#util" id="util">#</a></span><a aria-hidden="true" class="legacy" id="util_util"></a></h2> <p></p><div class="api_stability api_stability_2"><a href="documentation.html#stability-index">Stability: 2</a> - Stable</div><p></p> <p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v16.20.0/lib/util.js">lib/util.js</a></p> <p>The <code>node:util</code> module supports the needs of Node.js internal APIs. Many of the utilities are useful for application and module developers as well. To access it:</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);</code></pre> <section><h3><code>util.callbackify(original)</code><span><a class="mark" href="#utilcallbackifyoriginal" id="utilcallbackifyoriginal">#</a></span><a aria-hidden="true" class="legacy" id="util_util_callbackify_original"></a></h3> <div class="api_metadata"> <span>Added in: v8.2.0</span> </div> <ul> <li><code>original</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> An <code>async</code> function</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> a callback style function</li> </ul> <p>Takes an <code>async</code> function (or a function that returns a <code>Promise</code>) and returns a function following the error-first callback style, i.e. taking an <code>(err, value) => ...</code> callback as the last argument. In the callback, the first argument will be the rejection reason (or <code>null</code> if the <code>Promise</code> resolved), and the second argument will be the resolved value.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">fn</span>(<span class="hljs-params"></span>) { <span class="hljs-keyword">return</span> <span class="hljs-string">'hello world'</span>; } <span class="hljs-keyword">const</span> callbackFunction = util.<span class="hljs-title function_">callbackify</span>(fn); <span class="hljs-title function_">callbackFunction</span>(<span class="hljs-function">(<span class="hljs-params">err, ret</span>) =></span> { <span class="hljs-keyword">if</span> (err) <span class="hljs-keyword">throw</span> err; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(ret); });</code></pre> <p>Will print:</p> <pre><code class="language-text">hello world</code></pre> <p>The callback is executed asynchronously, and will have a limited stack trace. If the callback throws, the process will emit an <a href="process.html#event-uncaughtexception"><code>'uncaughtException'</code></a> event, and if not handled will exit.</p> <p>Since <code>null</code> has a special meaning as the first argument to a callback, if a wrapped function rejects a <code>Promise</code> with a falsy value as a reason, the value is wrapped in an <code>Error</code> with the original value stored in a field named <code>reason</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">function</span> <span class="hljs-title function_">fn</span>(<span class="hljs-params"></span>) { <span class="hljs-keyword">return</span> <span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">reject</span>(<span class="hljs-literal">null</span>); } <span class="hljs-keyword">const</span> callbackFunction = util.<span class="hljs-title function_">callbackify</span>(fn); <span class="hljs-title function_">callbackFunction</span>(<span class="hljs-function">(<span class="hljs-params">err, ret</span>) =></span> { <span class="hljs-comment">// When the Promise was rejected with `null` it is wrapped with an Error and</span> <span class="hljs-comment">// the original value is stored in `reason`.</span> err && <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">hasOwn</span>(err, <span class="hljs-string">'reason'</span>) && err.<span class="hljs-property">reason</span> === <span class="hljs-literal">null</span>; <span class="hljs-comment">// true</span> });</code></pre> </section><section><h3><code>util.debuglog(section[, callback])</code><span><a class="mark" href="#utildebuglogsection-callback" id="utildebuglogsection-callback">#</a></span><a aria-hidden="true" class="legacy" id="util_util_debuglog_section_callback"></a></h3> <div class="api_metadata"> <span>Added in: v0.11.3</span> </div> <ul> <li><code>section</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A string identifying the portion of the application for which the <code>debuglog</code> function is being created.</li> <li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A callback invoked the first time the logging function is called with a function argument that is a more optimized logging function.</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The logging function</li> </ul> <p>The <code>util.debuglog()</code> method is used to create a function that conditionally writes debug messages to <code>stderr</code> based on the existence of the <code>NODE_DEBUG</code> environment variable. If the <code>section</code> name appears within the value of that environment variable, then the returned function operates similar to <a href="console.html#consoleerrordata-args"><code>console.error()</code></a>. If not, then the returned function is a no-op.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> debuglog = util.<span class="hljs-title function_">debuglog</span>(<span class="hljs-string">'foo'</span>); <span class="hljs-title function_">debuglog</span>(<span class="hljs-string">'hello from foo [%d]'</span>, <span class="hljs-number">123</span>);</code></pre> <p>If this program is run with <code>NODE_DEBUG=foo</code> in the environment, then it will output something like:</p> <pre><code class="language-console">FOO 3245: hello from foo [123]</code></pre> <p>where <code>3245</code> is the process id. If it is not run with that environment variable set, then it will not print anything.</p> <p>The <code>section</code> supports wildcard also:</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> debuglog = util.<span class="hljs-title function_">debuglog</span>(<span class="hljs-string">'foo-bar'</span>); <span class="hljs-title function_">debuglog</span>(<span class="hljs-string">'hi there, it\'s foo-bar [%d]'</span>, <span class="hljs-number">2333</span>);</code></pre> <p>if it is run with <code>NODE_DEBUG=foo*</code> in the environment, then it will output something like:</p> <pre><code class="language-console">FOO-BAR 3257: hi there, it's foo-bar [2333]</code></pre> <p>Multiple comma-separated <code>section</code> names may be specified in the <code>NODE_DEBUG</code> environment variable: <code>NODE_DEBUG=fs,net,tls</code>.</p> <p>The optional <code>callback</code> argument can be used to replace the logging function with a different function that doesn't have any initialization or unnecessary wrapping.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">let</span> debuglog = util.<span class="hljs-title function_">debuglog</span>(<span class="hljs-string">'internals'</span>, <span class="hljs-function">(<span class="hljs-params">debug</span>) =></span> { <span class="hljs-comment">// Replace with a logging function that optimizes out</span> <span class="hljs-comment">// testing if the section is enabled</span> debuglog = debug; });</code></pre> <h4><code>debuglog().enabled</code><span><a class="mark" href="#debuglogenabled" id="debuglogenabled">#</a></span><a aria-hidden="true" class="legacy" id="util_debuglog_enabled"></a></h4> <div class="api_metadata"> <span>Added in: v14.9.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>The <code>util.debuglog().enabled</code> getter is used to create a test that can be used in conditionals based on the existence of the <code>NODE_DEBUG</code> environment variable. If the <code>section</code> name appears within the value of that environment variable, then the returned value will be <code>true</code>. If not, then the returned value will be <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> enabled = util.<span class="hljs-title function_">debuglog</span>(<span class="hljs-string">'foo'</span>).<span class="hljs-property">enabled</span>; <span class="hljs-keyword">if</span> (enabled) { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'hello from foo [%d]'</span>, <span class="hljs-number">123</span>); }</code></pre> <p>If this program is run with <code>NODE_DEBUG=foo</code> in the environment, then it will output something like:</p> <pre><code class="language-console">hello from foo [123]</code></pre> </section><section><h3><code>util.debug(section)</code><span><a class="mark" href="#utildebugsection" id="utildebugsection">#</a></span><a aria-hidden="true" class="legacy" id="util_util_debug_section"></a></h3> <div class="api_metadata"> <span>Added in: v14.9.0</span> </div> <p>Alias for <code>util.debuglog</code>. Usage allows for readability of that doesn't imply logging when only using <code>util.debuglog().enabled</code>.</p> </section><section><h3><code>util.deprecate(fn, msg[, code])</code><span><a class="mark" href="#utildeprecatefn-msg-code" id="utildeprecatefn-msg-code">#</a></span><a aria-hidden="true" class="legacy" id="util_util_deprecate_fn_msg_code"></a></h3> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v10.0.0</td> <td><p>Deprecation warnings are only emitted once for each code.</p></td></tr> <tr><td>v0.8.0</td> <td><p><span>Added in: v0.8.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The function that is being deprecated.</li> <li><code>msg</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A warning message to display when the deprecated function is invoked.</li> <li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A deprecation code. See the <a href="deprecations.html#list-of-deprecated-apis">list of deprecated APIs</a> for a list of codes.</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The deprecated function wrapped to emit a warning.</li> </ul> <p>The <code>util.deprecate()</code> method wraps <code>fn</code> (which may be a function or class) in such a way that it is marked as deprecated.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-built_in">exports</span>.<span class="hljs-property">obsoleteFunction</span> = util.<span class="hljs-title function_">deprecate</span>(<span class="hljs-function">() =></span> { <span class="hljs-comment">// Do something here.</span> }, <span class="hljs-string">'obsoleteFunction() is deprecated. Use newShinyFunction() instead.'</span>);</code></pre> <p>When called, <code>util.deprecate()</code> will return a function that will emit a <code>DeprecationWarning</code> using the <a href="process.html#event-warning"><code>'warning'</code></a> event. The warning will be emitted and printed to <code>stderr</code> the first time the returned function is called. After the warning is emitted, the wrapped function is called without emitting a warning.</p> <p>If the same optional <code>code</code> is supplied in multiple calls to <code>util.deprecate()</code>, the warning will be emitted only once for that <code>code</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> fn1 = util.<span class="hljs-title function_">deprecate</span>(someFunction, someMessage, <span class="hljs-string">'DEP0001'</span>); <span class="hljs-keyword">const</span> fn2 = util.<span class="hljs-title function_">deprecate</span>(someOtherFunction, someOtherMessage, <span class="hljs-string">'DEP0001'</span>); <span class="hljs-title function_">fn1</span>(); <span class="hljs-comment">// Emits a deprecation warning with code DEP0001</span> <span class="hljs-title function_">fn2</span>(); <span class="hljs-comment">// Does not emit a deprecation warning because it has the same code</span></code></pre> <p>If either the <code>--no-deprecation</code> or <code>--no-warnings</code> command-line flags are used, or if the <code>process.noDeprecation</code> property is set to <code>true</code> <em>prior</em> to the first deprecation warning, the <code>util.deprecate()</code> method does nothing.</p> <p>If the <code>--trace-deprecation</code> or <code>--trace-warnings</code> command-line flags are set, or the <code>process.traceDeprecation</code> property is set to <code>true</code>, a warning and a stack trace are printed to <code>stderr</code> the first time the deprecated function is called.</p> <p>If the <code>--throw-deprecation</code> command-line flag is set, or the <code>process.throwDeprecation</code> property is set to <code>true</code>, then an exception will be thrown when the deprecated function is called.</p> <p>The <code>--throw-deprecation</code> command-line flag and <code>process.throwDeprecation</code> property take precedence over <code>--trace-deprecation</code> and <code>process.traceDeprecation</code>.</p> </section><section><h3><code>util.format(format[, ...args])</code><span><a class="mark" href="#utilformatformat-args" id="utilformatformat-args">#</a></span><a aria-hidden="true" class="legacy" id="util_util_format_format_args"></a></h3> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v12.11.0</td> <td><p>The <code>%c</code> specifier is ignored now.</p></td></tr> <tr><td>v12.0.0</td> <td><p>The <code>format</code> argument is now only taken as such if it actually contains format specifiers.</p></td></tr> <tr><td>v12.0.0</td> <td><p>If the <code>format</code> argument is not a format string, the output string's formatting is no longer dependent on the type of the first argument. This change removes previously present quotes from strings that were being output when the first argument was not a string.</p></td></tr> <tr><td>v11.4.0</td> <td><p>The <code>%d</code>, <code>%f</code>, and <code>%i</code> specifiers now support Symbols properly.</p></td></tr> <tr><td>v11.4.0</td> <td><p>The <code>%o</code> specifier's <code>depth</code> has default depth of 4 again.</p></td></tr> <tr><td>v11.0.0</td> <td><p>The <code>%o</code> specifier's <code>depth</code> option will now fall back to the default depth.</p></td></tr> <tr><td>v10.12.0</td> <td><p>The <code>%d</code> and <code>%i</code> specifiers now support BigInt.</p></td></tr> <tr><td>v8.4.0</td> <td><p>The <code>%o</code> and <code>%O</code> specifiers are supported now.</p></td></tr> <tr><td>v0.5.3</td> <td><p><span>Added in: v0.5.3</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><code>format</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A <code>printf</code>-like format string.</li> </ul> <p>The <code>util.format()</code> method returns a formatted string using the first argument as a <code>printf</code>-like format string which can contain zero or more format specifiers. Each specifier is replaced with the converted value from the corresponding argument. Supported specifiers are:</p> <ul> <li><code>%s</code>: <code>String</code> will be used to convert all values except <code>BigInt</code>, <code>Object</code> and <code>-0</code>. <code>BigInt</code> values will be represented with an <code>n</code> and Objects that have no user defined <code>toString</code> function are inspected using <code>util.inspect()</code> with options <code>{ depth: 0, colors: false, compact: 3 }</code>.</li> <li><code>%d</code>: <code>Number</code> will be used to convert all values except <code>BigInt</code> and <code>Symbol</code>.</li> <li><code>%i</code>: <code>parseInt(value, 10)</code> is used for all values except <code>BigInt</code> and <code>Symbol</code>.</li> <li><code>%f</code>: <code>parseFloat(value)</code> is used for all values expect <code>Symbol</code>.</li> <li><code>%j</code>: JSON. Replaced with the string <code>'[Circular]'</code> if the argument contains circular references.</li> <li><code>%o</code>: <code>Object</code>. A string representation of an object with generic JavaScript object formatting. Similar to <code>util.inspect()</code> with options <code>{ showHidden: true, showProxy: true }</code>. This will show the full object including non-enumerable properties and proxies.</li> <li><code>%O</code>: <code>Object</code>. A string representation of an object with generic JavaScript object formatting. Similar to <code>util.inspect()</code> without options. This will show the full object not including non-enumerable properties and proxies.</li> <li><code>%c</code>: <code>CSS</code>. This specifier is ignored and will skip any CSS passed in.</li> <li><code>%%</code>: single percent sign (<code>'%'</code>). This does not consume an argument.</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The formatted string</li> </ul> <p>If a specifier does not have a corresponding argument, it is not replaced:</p> <pre><code class="language-js">util.<span class="hljs-title function_">format</span>(<span class="hljs-string">'%s:%s'</span>, <span class="hljs-string">'foo'</span>); <span class="hljs-comment">// Returns: 'foo:%s'</span></code></pre> <p>Values that are not part of the format string are formatted using <code>util.inspect()</code> if their type is not <code>string</code>.</p> <p>If there are more arguments passed to the <code>util.format()</code> method than the number of specifiers, the extra arguments are concatenated to the returned string, separated by spaces:</p> <pre><code class="language-js">util.<span class="hljs-title function_">format</span>(<span class="hljs-string">'%s:%s'</span>, <span class="hljs-string">'foo'</span>, <span class="hljs-string">'bar'</span>, <span class="hljs-string">'baz'</span>); <span class="hljs-comment">// Returns: 'foo:bar baz'</span></code></pre> <p>If the first argument does not contain a valid format specifier, <code>util.format()</code> returns a string that is the concatenation of all arguments separated by spaces:</p> <pre><code class="language-js">util.<span class="hljs-title function_">format</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>); <span class="hljs-comment">// Returns: '1 2 3'</span></code></pre> <p>If only one argument is passed to <code>util.format()</code>, it is returned as it is without any formatting:</p> <pre><code class="language-js">util.<span class="hljs-title function_">format</span>(<span class="hljs-string">'%% %s'</span>); <span class="hljs-comment">// Returns: '%% %s'</span></code></pre> <p><code>util.format()</code> is a synchronous method that is intended as a debugging tool. Some input values can have a significant performance overhead that can block the event loop. Use this function with care and never in a hot code path.</p> </section><section><h3><code>util.formatWithOptions(inspectOptions, format[, ...args])</code><span><a class="mark" href="#utilformatwithoptionsinspectoptions-format-args" id="utilformatwithoptionsinspectoptions-format-args">#</a></span><a aria-hidden="true" class="legacy" id="util_util_formatwithoptions_inspectoptions_format_args"></a></h3> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>inspectOptions</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> <li><code>format</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>This function is identical to <a href="#utilformatformat-args"><code>util.format()</code></a>, except in that it takes an <code>inspectOptions</code> argument which specifies options that are passed along to <a href="#utilinspectobject-options"><code>util.inspect()</code></a>.</p> <pre><code class="language-js">util.<span class="hljs-title function_">formatWithOptions</span>({ <span class="hljs-attr">colors</span>: <span class="hljs-literal">true</span> }, <span class="hljs-string">'See object %O'</span>, { <span class="hljs-attr">foo</span>: <span class="hljs-number">42</span> }); <span class="hljs-comment">// Returns 'See object { foo: 42 }', where `42` is colored as a number</span> <span class="hljs-comment">// when printed to a terminal.</span></code></pre> </section><section><h3><code>util.getSystemErrorName(err)</code><span><a class="mark" href="#utilgetsystemerrornameerr" id="utilgetsystemerrornameerr">#</a></span><a aria-hidden="true" class="legacy" id="util_util_getsystemerrorname_err"></a></h3> <div class="api_metadata"> <span>Added in: v9.7.0</span> </div> <ul> <li><code>err</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>Returns the string name for a numeric error code that comes from a Node.js API. The mapping between error codes and error names is platform-dependent. See <a href="errors.html#common-system-errors">Common System Errors</a> for the names of common errors.</p> <pre><code class="language-js">fs.<span class="hljs-title function_">access</span>(<span class="hljs-string">'file/that/does/not/exist'</span>, <span class="hljs-function">(<span class="hljs-params">err</span>) =></span> { <span class="hljs-keyword">const</span> name = util.<span class="hljs-title function_">getSystemErrorName</span>(err.<span class="hljs-property">errno</span>); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(name); <span class="hljs-comment">// ENOENT</span> });</code></pre> </section><section><h3><code>util.getSystemErrorMap()</code><span><a class="mark" href="#utilgetsystemerrormap" id="utilgetsystemerrormap">#</a></span><a aria-hidden="true" class="legacy" id="util_util_getsystemerrormap"></a></h3> <div class="api_metadata"> <span>Added in: v16.0.0</span> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map" class="type"><Map></a></li> </ul> <p>Returns a Map of all system error codes available from the Node.js API. The mapping between error codes and error names is platform-dependent. See <a href="errors.html#common-system-errors">Common System Errors</a> for the names of common errors.</p> <pre><code class="language-js">fs.<span class="hljs-title function_">access</span>(<span class="hljs-string">'file/that/does/not/exist'</span>, <span class="hljs-function">(<span class="hljs-params">err</span>) =></span> { <span class="hljs-keyword">const</span> errorMap = util.<span class="hljs-title function_">getSystemErrorMap</span>(); <span class="hljs-keyword">const</span> name = errorMap.<span class="hljs-title function_">get</span>(err.<span class="hljs-property">errno</span>); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(name); <span class="hljs-comment">// ENOENT</span> });</code></pre> </section><section><h3><code>util.inherits(constructor, superConstructor)</code><span><a class="mark" href="#utilinheritsconstructor-superconstructor" id="utilinheritsconstructor-superconstructor">#</a></span><a aria-hidden="true" class="legacy" id="util_util_inherits_constructor_superconstructor"></a></h3> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v5.0.0</td> <td><p>The <code>constructor</code> parameter can refer to an ES6 class now.</p></td></tr> <tr><td>v0.3.0</td> <td><p><span>Added in: v0.3.0</span></p></td></tr> </tbody></table> </details> </div> <p></p><div class="api_stability api_stability_3"><a href="documentation.html#stability-index">Stability: 3</a> - Legacy: Use ES2015 class syntax and <code>extends</code> keyword instead.</div><p></p> <ul> <li><code>constructor</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> <li><code>superConstructor</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> </ul> <p>Usage of <code>util.inherits()</code> is discouraged. Please use the ES6 <code>class</code> and <code>extends</code> keywords to get language level inheritance support. Also note that the two styles are <a href="https://github.com/nodejs/node/issues/4179">semantically incompatible</a>.</p> <p>Inherit the prototype methods from one <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/constructor">constructor</a> into another. The prototype of <code>constructor</code> will be set to a new object created from <code>superConstructor</code>.</p> <p>This mainly adds some input validation on top of <code>Object.setPrototypeOf(constructor.prototype, superConstructor.prototype)</code>. As an additional convenience, <code>superConstructor</code> will be accessible through the <code>constructor.super_</code> property.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> <span class="hljs-title class_">EventEmitter</span> = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:events'</span>); <span class="hljs-keyword">function</span> <span class="hljs-title function_">MyStream</span>(<span class="hljs-params"></span>) { <span class="hljs-title class_">EventEmitter</span>.<span class="hljs-title function_">call</span>(<span class="hljs-variable language_">this</span>); } util.<span class="hljs-title function_">inherits</span>(<span class="hljs-title class_">MyStream</span>, <span class="hljs-title class_">EventEmitter</span>); <span class="hljs-title class_">MyStream</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>.<span class="hljs-property">write</span> = <span class="hljs-keyword">function</span>(<span class="hljs-params">data</span>) { <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emit</span>(<span class="hljs-string">'data'</span>, data); }; <span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MyStream</span>(); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(stream <span class="hljs-keyword">instanceof</span> <span class="hljs-title class_">EventEmitter</span>); <span class="hljs-comment">// true</span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">MyStream</span>.<span class="hljs-property">super_</span> === <span class="hljs-title class_">EventEmitter</span>); <span class="hljs-comment">// true</span> stream.<span class="hljs-title function_">on</span>(<span class="hljs-string">'data'</span>, <span class="hljs-function">(<span class="hljs-params">data</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Received data: "<span class="hljs-subst">${data}</span>"`</span>); }); stream.<span class="hljs-title function_">write</span>(<span class="hljs-string">'It works!'</span>); <span class="hljs-comment">// Received data: "It works!"</span></code></pre> <p>ES6 example using <code>class</code> and <code>extends</code>:</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> <span class="hljs-title class_">EventEmitter</span> = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:events'</span>); <span class="hljs-keyword">class</span> <span class="hljs-title class_">MyStream</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_ inherited__">EventEmitter</span> { <span class="hljs-title function_">write</span>(<span class="hljs-params">data</span>) { <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emit</span>(<span class="hljs-string">'data'</span>, data); } } <span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MyStream</span>(); stream.<span class="hljs-title function_">on</span>(<span class="hljs-string">'data'</span>, <span class="hljs-function">(<span class="hljs-params">data</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Received data: "<span class="hljs-subst">${data}</span>"`</span>); }); stream.<span class="hljs-title function_">write</span>(<span class="hljs-string">'With ES6'</span>);</code></pre> </section><section><h3><code>util.inspect(object[, options])</code><span><a class="mark" href="#utilinspectobject-options" id="utilinspectobject-options">#</a></span><a aria-hidden="true" class="legacy" id="util_util_inspect_object_options"></a></h3> </section><section><h3><code>util.inspect(object[, showHidden[, depth[, colors]]])</code><span><a class="mark" href="#utilinspectobject-showhidden-depth-colors" id="utilinspectobject-showhidden-depth-colors">#</a></span><a aria-hidden="true" class="legacy" id="util_util_inspect_object_showhidden_depth_colors"></a></h3> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v16.18.0</td> <td><p>add support for <code>maxArrayLength</code> when inspecting <code>Set</code> and <code>Map</code>.</p></td></tr> <tr><td>v16.14.0</td> <td><p>The <code>numericSeparator</code> option is supported now.</p></td></tr> <tr><td>v13.0.0</td> <td><p>Circular references now include a marker to the reference.</p></td></tr> <tr><td>v14.6.0, v12.19.0</td> <td><p>If <code>object</code> is from a different <code>vm.Context</code> now, a custom inspection function on it will not receive context-specific arguments anymore.</p></td></tr> <tr><td>v13.13.0, v12.17.0</td> <td><p>The <code>maxStringLength</code> option is supported now.</p></td></tr> <tr><td>v13.5.0, v12.16.0</td> <td><p>User defined prototype properties are inspected in case <code>showHidden</code> is <code>true</code>.</p></td></tr> <tr><td>v12.0.0</td> <td><p>The <code>compact</code> options default is changed to <code>3</code> and the <code>breakLength</code> options default is changed to <code>80</code>.</p></td></tr> <tr><td>v12.0.0</td> <td><p>Internal properties no longer appear in the context argument of a custom inspection function.</p></td></tr> <tr><td>v11.11.0</td> <td><p>The <code>compact</code> option accepts numbers for a new output mode.</p></td></tr> <tr><td>v11.7.0</td> <td><p>ArrayBuffers now also show their binary contents.</p></td></tr> <tr><td>v11.5.0</td> <td><p>The <code>getters</code> option is supported now.</p></td></tr> <tr><td>v11.4.0</td> <td><p>The <code>depth</code> default changed back to <code>2</code>.</p></td></tr> <tr><td>v11.0.0</td> <td><p>The <code>depth</code> default changed to <code>20</code>.</p></td></tr> <tr><td>v11.0.0</td> <td><p>The inspection output is now limited to about 128 MiB. Data above that size will not be fully inspected.</p></td></tr> <tr><td>v10.12.0</td> <td><p>The <code>sorted</code> option is supported now.</p></td></tr> <tr><td>v10.6.0</td> <td><p>Inspecting linked lists and similar objects is now possible up to the maximum call stack size.</p></td></tr> <tr><td>v10.0.0</td> <td><p>The <code>WeakMap</code> and <code>WeakSet</code> entries can now be inspected as well.</p></td></tr> <tr><td>v9.9.0</td> <td><p>The <code>compact</code> option is supported now.</p></td></tr> <tr><td>v6.6.0</td> <td><p>Custom inspection functions can now return <code>this</code>.</p></td></tr> <tr><td>v6.3.0</td> <td><p>The <code>breakLength</code> option is supported now.</p></td></tr> <tr><td>v6.1.0</td> <td><p>The <code>maxArrayLength</code> option is supported now; in particular, long arrays are truncated by default.</p></td></tr> <tr><td>v6.1.0</td> <td><p>The <code>showProxy</code> option is supported now.</p></td></tr> <tr><td>v0.3.0</td> <td><p><span>Added in: v0.3.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Any JavaScript primitive or <code>Object</code>.</li> <li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> <ul> <li><code>showHidden</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, <code>object</code>'s non-enumerable symbols and properties are included in the formatted result. <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> entries are also included as well as user defined prototype properties (excluding method properties). <strong>Default:</strong> <code>false</code>.</li> <li><code>depth</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Specifies the number of times to recurse while formatting <code>object</code>. This is useful for inspecting large objects. To recurse up to the maximum call stack size pass <code>Infinity</code> or <code>null</code>. <strong>Default:</strong> <code>2</code>.</li> <li><code>colors</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, the output is styled with ANSI color codes. Colors are customizable. See <a href="#customizing-utilinspect-colors">Customizing <code>util.inspect</code> colors</a>. <strong>Default:</strong> <code>false</code>.</li> <li><code>customInspect</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>false</code>, <code>[util.inspect.custom](depth, opts, inspect)</code> functions are not invoked. <strong>Default:</strong> <code>true</code>.</li> <li><code>showProxy</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, <code>Proxy</code> inspection includes the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy#Terminology"><code>target</code> and <code>handler</code></a> objects. <strong>Default:</strong> <code>false</code>.</li> <li><code>maxArrayLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> Specifies the maximum number of <code>Array</code>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray"><code>TypedArray</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a>, and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> elements to include when formatting. Set to <code>null</code> or <code>Infinity</code> to show all elements. Set to <code>0</code> or negative to show no elements. <strong>Default:</strong> <code>100</code>.</li> <li><code>maxStringLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> Specifies the maximum number of characters to include when formatting. Set to <code>null</code> or <code>Infinity</code> to show all elements. Set to <code>0</code> or negative to show no characters. <strong>Default:</strong> <code>10000</code>.</li> <li><code>breakLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> The length at which input values are split across multiple lines. Set to <code>Infinity</code> to format the input as a single line (in combination with <code>compact</code> set to <code>true</code> or any number >= <code>1</code>). <strong>Default:</strong> <code>80</code>.</li> <li><code>compact</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> Setting this to <code>false</code> causes each object key to be displayed on a new line. It will break on new lines in text that is longer than <code>breakLength</code>. If set to a number, the most <code>n</code> inner elements are united on a single line as long as all properties fit into <code>breakLength</code>. Short array elements are also grouped together. For more information, see the example below. <strong>Default:</strong> <code>3</code>.</li> <li><code>sorted</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> If set to <code>true</code> or a function, all properties of an object, and <code>Set</code> and <code>Map</code> entries are sorted in the resulting string. If set to <code>true</code> the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort">default sort</a> is used. If set to a function, it is used as a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort#Parameters">compare function</a>.</li> <li><code>getters</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> If set to <code>true</code>, getters are inspected. If set to <code>'get'</code>, only getters without a corresponding setter are inspected. If set to <code>'set'</code>, only getters with a corresponding setter are inspected. This might cause side effects depending on the getter function. <strong>Default:</strong> <code>false</code>.</li> <li><code>numericSeparator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If set to <code>true</code>, an underscore is used to separate every three digits in all bigints and numbers. <strong>Default:</strong> <code>false</code>.</li> </ul> </li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The representation of <code>object</code>.</li> </ul> <p>The <code>util.inspect()</code> method returns a string representation of <code>object</code> that is intended for debugging. The output of <code>util.inspect</code> may change at any time and should not be depended upon programmatically. Additional <code>options</code> may be passed that alter the result. <code>util.inspect()</code> will use the constructor's name and/or <code>@@toStringTag</code> to make an identifiable tag for an inspected value.</p> <pre><code class="language-js"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Foo</span> { get [<span class="hljs-title class_">Symbol</span>.<span class="hljs-property">toStringTag</span>]() { <span class="hljs-keyword">return</span> <span class="hljs-string">'bar'</span>; } } <span class="hljs-keyword">class</span> <span class="hljs-title class_">Bar</span> {} <span class="hljs-keyword">const</span> baz = <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">create</span>(<span class="hljs-literal">null</span>, { [<span class="hljs-title class_">Symbol</span>.<span class="hljs-property">toStringTag</span>]: { <span class="hljs-attr">value</span>: <span class="hljs-string">'foo'</span> } }); util.<span class="hljs-title function_">inspect</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Foo</span>()); <span class="hljs-comment">// 'Foo [bar] {}'</span> util.<span class="hljs-title function_">inspect</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Bar</span>()); <span class="hljs-comment">// 'Bar {}'</span> util.<span class="hljs-title function_">inspect</span>(baz); <span class="hljs-comment">// '[foo] {}'</span></code></pre> <p>Circular references point to their anchor by using a reference index:</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { inspect } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> obj = {}; obj.<span class="hljs-property">a</span> = [obj]; obj.<span class="hljs-property">b</span> = {}; obj.<span class="hljs-property">b</span>.<span class="hljs-property">inner</span> = obj.<span class="hljs-property">b</span>; obj.<span class="hljs-property">b</span>.<span class="hljs-property">obj</span> = obj; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">inspect</span>(obj)); <span class="hljs-comment">// <ref *1> {</span> <span class="hljs-comment">// a: [ [Circular *1] ],</span> <span class="hljs-comment">// b: <ref *2> { inner: [Circular *2], obj: [Circular *1] }</span> <span class="hljs-comment">// }</span></code></pre> <p>The following example inspects all properties of the <code>util</code> object:</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-title function_">inspect</span>(util, { <span class="hljs-attr">showHidden</span>: <span class="hljs-literal">true</span>, <span class="hljs-attr">depth</span>: <span class="hljs-literal">null</span> }));</code></pre> <p>The following example highlights the effect of the <code>compact</code> option:</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> o = { <span class="hljs-attr">a</span>: [<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, [[ <span class="hljs-string">'Lorem ipsum dolor sit amet,\nconsectetur adipiscing elit, sed do '</span> + <span class="hljs-string">'eiusmod \ntempor incididunt ut labore et dolore magna aliqua.'</span>, <span class="hljs-string">'test'</span>, <span class="hljs-string">'foo'</span>]], <span class="hljs-number">4</span>], <span class="hljs-attr">b</span>: <span class="hljs-keyword">new</span> <span class="hljs-title class_">Map</span>([[<span class="hljs-string">'za'</span>, <span class="hljs-number">1</span>], [<span class="hljs-string">'zb'</span>, <span class="hljs-string">'test'</span>]]) }; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-title function_">inspect</span>(o, { <span class="hljs-attr">compact</span>: <span class="hljs-literal">true</span>, <span class="hljs-attr">depth</span>: <span class="hljs-number">5</span>, <span class="hljs-attr">breakLength</span>: <span class="hljs-number">80</span> })); <span class="hljs-comment">// { a:</span> <span class="hljs-comment">// [ 1,</span> <span class="hljs-comment">// 2,</span> <span class="hljs-comment">// [ [ 'Lorem ipsum dolor sit amet,\nconsectetur [...]', // A long line</span> <span class="hljs-comment">// 'test',</span> <span class="hljs-comment">// 'foo' ] ],</span> <span class="hljs-comment">// 4 ],</span> <span class="hljs-comment">// b: Map(2) { 'za' => 1, 'zb' => 'test' } }</span> <span class="hljs-comment">// Setting `compact` to false or an integer creates more reader friendly output.</span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-title function_">inspect</span>(o, { <span class="hljs-attr">compact</span>: <span class="hljs-literal">false</span>, <span class="hljs-attr">depth</span>: <span class="hljs-number">5</span>, <span class="hljs-attr">breakLength</span>: <span class="hljs-number">80</span> })); <span class="hljs-comment">// {</span> <span class="hljs-comment">// a: [</span> <span class="hljs-comment">// 1,</span> <span class="hljs-comment">// 2,</span> <span class="hljs-comment">// [</span> <span class="hljs-comment">// [</span> <span class="hljs-comment">// 'Lorem ipsum dolor sit amet,\n' +</span> <span class="hljs-comment">// 'consectetur adipiscing elit, sed do eiusmod \n' +</span> <span class="hljs-comment">// 'tempor incididunt ut labore et dolore magna aliqua.',</span> <span class="hljs-comment">// 'test',</span> <span class="hljs-comment">// 'foo'</span> <span class="hljs-comment">// ]</span> <span class="hljs-comment">// ],</span> <span class="hljs-comment">// 4</span> <span class="hljs-comment">// ],</span> <span class="hljs-comment">// b: Map(2) {</span> <span class="hljs-comment">// 'za' => 1,</span> <span class="hljs-comment">// 'zb' => 'test'</span> <span class="hljs-comment">// }</span> <span class="hljs-comment">// }</span> <span class="hljs-comment">// Setting `breakLength` to e.g. 150 will print the "Lorem ipsum" text in a</span> <span class="hljs-comment">// single line.</span></code></pre> <p>The <code>showHidden</code> option allows <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> entries to be inspected. If there are more entries than <code>maxArrayLength</code>, there is no guarantee which entries are displayed. That means retrieving the same <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> entries twice may result in different output. Furthermore, entries with no remaining strong references may be garbage collected at any time.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { inspect } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> obj = { <span class="hljs-attr">a</span>: <span class="hljs-number">1</span> }; <span class="hljs-keyword">const</span> obj2 = { <span class="hljs-attr">b</span>: <span class="hljs-number">2</span> }; <span class="hljs-keyword">const</span> weakSet = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakSet</span>([obj, obj2]); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">inspect</span>(weakSet, { <span class="hljs-attr">showHidden</span>: <span class="hljs-literal">true</span> })); <span class="hljs-comment">// WeakSet { { a: 1 }, { b: 2 } }</span></code></pre> <p>The <code>sorted</code> option ensures that an object's property insertion order does not impact the result of <code>util.inspect()</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { inspect } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>); <span class="hljs-keyword">const</span> o1 = { <span class="hljs-attr">b</span>: [<span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">1</span>], <span class="hljs-attr">a</span>: <span class="hljs-string">'`a` comes before `b`'</span>, <span class="hljs-attr">c</span>: <span class="hljs-keyword">new</span> <span class="hljs-title class_">Set</span>([<span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">1</span>]) }; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">inspect</span>(o1, { <span class="hljs-attr">sorted</span>: <span class="hljs-literal">true</span> })); <span class="hljs-comment">// { a: '`a` comes before `b`', b: [ 2, 3, 1 ], c: Set(3) { 1, 2, 3 } }</span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">inspect</span>(o1, { <span class="hljs-attr">sorted</span>: <span class="hljs-function">(<span class="hljs-params">a, b</span>) =></span> b.<span class="hljs-title function_">localeCompare</span>(a) })); <span class="hljs-comment">// { c: Set(3) { 3, 2, 1 }, b: [ 2, 3, 1 ], a: '`a` comes before `b`' }</span> <span class="hljs-keyword">const</span> o2 = { <span class="hljs-attr">c</span>: <span class="hljs-keyword">new</span> <span class="hljs-title class_">Set</span>([<span class="hljs-number">2</span>, <span class="hljs-number">1</span>, <span class="hljs-number">3</span>]), <span class="hljs-attr">a</span>: <span class="hljs-string">'`a` comes before `b`'</span>, <span class="hljs-attr">b</span>: [<span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">1</span>] }; assert.<span class="hljs-property">strict</span>.<span class="hljs-title function_">equal</span>( <span class="hljs-title function_">inspect</span>(o1, { <span class="hljs-attr">sorted</span>: <span class="hljs-literal">true</span> }), <span class="hljs-title function_">inspect</span>(o2, { <span class="hljs-attr">sorted</span>: <span class="hljs-literal">true</span> }) );</code></pre> <p>The <code>numericSeparator</code> option adds an underscore every three digits to all numbers.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { inspect } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> thousand = <span class="hljs-number">1_000</span>; <span class="hljs-keyword">const</span> million = <span class="hljs-number">1_000_000</span>; <span class="hljs-keyword">const</span> bigNumber = <span class="hljs-number">123_456_789n</span>; <span class="hljs-keyword">const</span> bigDecimal = <span class="hljs-number">1_234.123_45</span>; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(thousand, million, bigNumber, bigDecimal); <span class="hljs-comment">// 1_000 1_000_000 123_456_789n 1_234.123_45</span></code></pre> <p><code>util.inspect()</code> is a synchronous method intended for debugging. Its maximum output length is approximately 128 MiB. Inputs that result in longer output will be truncated.</p> <h4>Customizing <code>util.inspect</code> colors<span><a class="mark" href="#customizing-utilinspect-colors" id="customizing-utilinspect-colors">#</a></span><a aria-hidden="true" class="legacy" id="util_customizing_util_inspect_colors"></a></h4> <p>Color output (if enabled) of <code>util.inspect</code> is customizable globally via the <code>util.inspect.styles</code> and <code>util.inspect.colors</code> properties.</p> <p><code>util.inspect.styles</code> is a map associating a style name to a color from <code>util.inspect.colors</code>.</p> <p>The default styles and associated colors are:</p> <ul> <li><code>bigint</code>: <code>yellow</code></li> <li><code>boolean</code>: <code>yellow</code></li> <li><code>date</code>: <code>magenta</code></li> <li><code>module</code>: <code>underline</code></li> <li><code>name</code>: (no styling)</li> <li><code>null</code>: <code>bold</code></li> <li><code>number</code>: <code>yellow</code></li> <li><code>regexp</code>: <code>red</code></li> <li><code>special</code>: <code>cyan</code> (e.g., <code>Proxies</code>)</li> <li><code>string</code>: <code>green</code></li> <li><code>symbol</code>: <code>green</code></li> <li><code>undefined</code>: <code>grey</code></li> </ul> <p>Color styling uses ANSI control codes that may not be supported on all terminals. To verify color support use <a href="tty.html#writestreamhascolorscount-env"><code>tty.hasColors()</code></a>.</p> <p>Predefined control codes are listed below (grouped as "Modifiers", "Foreground colors", and "Background colors").</p> <h5>Modifiers<span><a class="mark" href="#modifiers" id="modifiers">#</a></span><a aria-hidden="true" class="legacy" id="util_modifiers"></a></h5> <p>Modifier support varies throughout different terminals. They will mostly be ignored, if not supported.</p> <ul> <li><code>reset</code> - Resets all (color) modifiers to their defaults</li> <li><strong>bold</strong> - Make text bold</li> <li><em>italic</em> - Make text italic</li> <li><span style="border-bottom: 1px;">underline</span> - Make text underlined</li> <li><del>strikethrough</del> - Puts a horizontal line through the center of the text (Alias: <code>strikeThrough</code>, <code>crossedout</code>, <code>crossedOut</code>)</li> <li><code>hidden</code> - Prints the text, but makes it invisible (Alias: conceal)</li> <li><span style="opacity: 0.5;">dim</span> - Decreased color intensity (Alias: <code>faint</code>)</li> <li><span style="border-top: 1px">overlined</span> - Make text overlined</li> <li>blink - Hides and shows the text in an interval</li> <li><span style="filter: invert(100%)">inverse</span> - Swap foreground and background colors (Alias: <code>swapcolors</code>, <code>swapColors</code>)</li> <li><span style="border-bottom: 1px double;">doubleunderline</span> - Make text double underlined (Alias: <code>doubleUnderline</code>)</li> <li><span style="border: 1px">framed</span> - Draw a frame around the text</li> </ul> <h5>Foreground colors<span><a class="mark" href="#foreground-colors" id="foreground-colors">#</a></span><a aria-hidden="true" class="legacy" id="util_foreground_colors"></a></h5> <ul> <li><code>black</code></li> <li><code>red</code></li> <li><code>green</code></li> <li><code>yellow</code></li> <li><code>blue</code></li> <li><code>magenta</code></li> <li><code>cyan</code></li> <li><code>white</code></li> <li><code>gray</code> (alias: <code>grey</code>, <code>blackBright</code>)</li> <li><code>redBright</code></li> <li><code>greenBright</code></li> <li><code>yellowBright</code></li> <li><code>blueBright</code></li> <li><code>magentaBright</code></li> <li><code>cyanBright</code></li> <li><code>whiteBright</code></li> </ul> <h5>Background colors<span><a class="mark" href="#background-colors" id="background-colors">#</a></span><a aria-hidden="true" class="legacy" id="util_background_colors"></a></h5> <ul> <li><code>bgBlack</code></li> <li><code>bgRed</code></li> <li><code>bgGreen</code></li> <li><code>bgYellow</code></li> <li><code>bgBlue</code></li> <li><code>bgMagenta</code></li> <li><code>bgCyan</code></li> <li><code>bgWhite</code></li> <li><code>bgGray</code> (alias: <code>bgGrey</code>, <code>bgBlackBright</code>)</li> <li><code>bgRedBright</code></li> <li><code>bgGreenBright</code></li> <li><code>bgYellowBright</code></li> <li><code>bgBlueBright</code></li> <li><code>bgMagentaBright</code></li> <li><code>bgCyanBright</code></li> <li><code>bgWhiteBright</code></li> </ul> <h4>Custom inspection functions on objects<span><a class="mark" href="#custom-inspection-functions-on-objects" id="custom-inspection-functions-on-objects">#</a></span><a aria-hidden="true" class="legacy" id="util_custom_inspection_functions_on_objects"></a></h4> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v16.14.0</td> <td><p>The inspect argument is added for more interoperability.</p></td></tr> <tr><td>v0.1.97</td> <td><p><span>Added in: v0.1.97</span></p></td></tr> </tbody></table> </details> </div> <p>Objects may also define their own <a href="#utilinspectcustom"><code>[util.inspect.custom](depth, opts, inspect)</code></a> function, which <code>util.inspect()</code> will invoke and use the result of when inspecting the object.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">class</span> <span class="hljs-title class_">Box</span> { <span class="hljs-title function_">constructor</span>(<span class="hljs-params">value</span>) { <span class="hljs-variable language_">this</span>.<span class="hljs-property">value</span> = value; } [util.<span class="hljs-property">inspect</span>.<span class="hljs-property">custom</span>](depth, options, inspect) { <span class="hljs-keyword">if</span> (depth < <span class="hljs-number">0</span>) { <span class="hljs-keyword">return</span> options.<span class="hljs-title function_">stylize</span>(<span class="hljs-string">'[Box]'</span>, <span class="hljs-string">'special'</span>); } <span class="hljs-keyword">const</span> newOptions = <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">assign</span>({}, options, { <span class="hljs-attr">depth</span>: options.<span class="hljs-property">depth</span> === <span class="hljs-literal">null</span> ? <span class="hljs-literal">null</span> : options.<span class="hljs-property">depth</span> - <span class="hljs-number">1</span> }); <span class="hljs-comment">// Five space padding because that's the size of "Box< ".</span> <span class="hljs-keyword">const</span> padding = <span class="hljs-string">' '</span>.<span class="hljs-title function_">repeat</span>(<span class="hljs-number">5</span>); <span class="hljs-keyword">const</span> inner = <span class="hljs-title function_">inspect</span>(<span class="hljs-variable language_">this</span>.<span class="hljs-property">value</span>, newOptions) .<span class="hljs-title function_">replace</span>(<span class="hljs-regexp">/\n/g</span>, <span class="hljs-string">`\n<span class="hljs-subst">${padding}</span>`</span>); <span class="hljs-keyword">return</span> <span class="hljs-string">`<span class="hljs-subst">${options.stylize(<span class="hljs-string">'Box'</span>, <span class="hljs-string">'special'</span>)}</span>< <span class="hljs-subst">${inner}</span> >`</span>; } } <span class="hljs-keyword">const</span> box = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Box</span>(<span class="hljs-literal">true</span>); util.<span class="hljs-title function_">inspect</span>(box); <span class="hljs-comment">// Returns: "Box< true >"</span></code></pre> <p>Custom <code>[util.inspect.custom](depth, opts, inspect)</code> functions typically return a string but may return a value of any type that will be formatted accordingly by <code>util.inspect()</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> obj = { <span class="hljs-attr">foo</span>: <span class="hljs-string">'this will not show up in the inspect() output'</span> }; obj[util.<span class="hljs-property">inspect</span>.<span class="hljs-property">custom</span>] = <span class="hljs-function">(<span class="hljs-params">depth</span>) =></span> { <span class="hljs-keyword">return</span> { <span class="hljs-attr">bar</span>: <span class="hljs-string">'baz'</span> }; }; util.<span class="hljs-title function_">inspect</span>(obj); <span class="hljs-comment">// Returns: "{ bar: 'baz' }"</span></code></pre> <h4><code>util.inspect.custom</code><span><a class="mark" href="#utilinspectcustom" id="utilinspectcustom">#</a></span><a aria-hidden="true" class="legacy" id="util_util_inspect_custom"></a></h4> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v10.12.0</td> <td><p>This is now defined as a shared symbol.</p></td></tr> <tr><td>v6.6.0</td> <td><p><span>Added in: v6.6.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type" class="type"><symbol></a> that can be used to declare custom inspect functions.</li> </ul> <p>In addition to being accessible through <code>util.inspect.custom</code>, this symbol is <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/for">registered globally</a> and can be accessed in any environment as <code>Symbol.for('nodejs.util.inspect.custom')</code>.</p> <p>Using this allows code to be written in a portable fashion, so that the custom inspect function is used in an Node.js environment and ignored in the browser. The <code>util.inspect()</code> function itself is passed as third argument to the custom inspect function to allow further portability.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> customInspectSymbol = <span class="hljs-title class_">Symbol</span>.<span class="hljs-title function_">for</span>(<span class="hljs-string">'nodejs.util.inspect.custom'</span>); <span class="hljs-keyword">class</span> <span class="hljs-title class_">Password</span> { <span class="hljs-title function_">constructor</span>(<span class="hljs-params">value</span>) { <span class="hljs-variable language_">this</span>.<span class="hljs-property">value</span> = value; } <span class="hljs-title function_">toString</span>(<span class="hljs-params"></span>) { <span class="hljs-keyword">return</span> <span class="hljs-string">'xxxxxxxx'</span>; } [customInspectSymbol](depth, inspectOptions, inspect) { <span class="hljs-keyword">return</span> <span class="hljs-string">`Password <<span class="hljs-subst">${<span class="hljs-variable language_">this</span>.toString()}</span>>`</span>; } } <span class="hljs-keyword">const</span> password = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Password</span>(<span class="hljs-string">'r0sebud'</span>); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(password); <span class="hljs-comment">// Prints Password <xxxxxxxx></span></code></pre> <p>See <a href="#custom-inspection-functions-on-objects">Custom inspection functions on Objects</a> for more details.</p> <h4><code>util.inspect.defaultOptions</code><span><a class="mark" href="#utilinspectdefaultoptions" id="utilinspectdefaultoptions">#</a></span><a aria-hidden="true" class="legacy" id="util_util_inspect_defaultoptions"></a></h4> <div class="api_metadata"> <span>Added in: v6.4.0</span> </div> <p>The <code>defaultOptions</code> value allows customization of the default options used by <code>util.inspect</code>. This is useful for functions like <code>console.log</code> or <code>util.format</code> which implicitly call into <code>util.inspect</code>. It shall be set to an object containing one or more valid <a href="#utilinspectobject-options"><code>util.inspect()</code></a> options. Setting option properties directly is also supported.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> arr = <span class="hljs-title class_">Array</span>(<span class="hljs-number">101</span>).<span class="hljs-title function_">fill</span>(<span class="hljs-number">0</span>); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(arr); <span class="hljs-comment">// Logs the truncated array</span> util.<span class="hljs-property">inspect</span>.<span class="hljs-property">defaultOptions</span>.<span class="hljs-property">maxArrayLength</span> = <span class="hljs-literal">null</span>; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(arr); <span class="hljs-comment">// logs the full array</span></code></pre> </section><section><h3><code>util.isDeepStrictEqual(val1, val2)</code><span><a class="mark" href="#utilisdeepstrictequalval1-val2" id="utilisdeepstrictequalval1-val2">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isdeepstrictequal_val1_val2"></a></h3> <div class="api_metadata"> <span>Added in: v9.0.0</span> </div> <ul> <li><code>val1</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li><code>val2</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if there is deep strict equality between <code>val1</code> and <code>val2</code>. Otherwise, returns <code>false</code>.</p> <p>See <a href="assert.html#assertdeepstrictequalactual-expected-message"><code>assert.deepStrictEqual()</code></a> for more information about deep strict equality.</p> </section><section><h3><code>util.parseArgs([config])</code><span><a class="mark" href="#utilparseargsconfig" id="utilparseargsconfig">#</a></span><a aria-hidden="true" class="legacy" id="util_util_parseargs_config"></a></h3> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v16.19.0</td> <td><p>Add support for default values in input <code>config</code>.</p></td></tr> <tr><td>v16.17.0</td> <td><p>add support for returning detailed parse information using <code>tokens</code> in input <code>config</code> and returned properties.</p></td></tr> <tr><td>v16.17.0</td> <td><p><span>Added in: v16.17.0</span></p></td></tr> </tbody></table> </details> </div> <p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p> <ul> <li> <p><code>config</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Used to provide arguments for parsing and to configure the parser. <code>config</code> supports the following properties:</p> <ul> <li><code>args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> array of argument strings. <strong>Default:</strong> <code>process.argv</code> with <code>execPath</code> and <code>filename</code> removed.</li> <li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Used to describe arguments known to the parser. Keys of <code>options</code> are the long names of options and values are an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> accepting the following properties: <ul> <li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Type of argument, which must be either <code>boolean</code> or <code>string</code>.</li> <li><code>multiple</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Whether this option can be provided multiple times. If <code>true</code>, all values will be collected in an array. If <code>false</code>, values for the option are last-wins. <strong>Default:</strong> <code>false</code>.</li> <li><code>short</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A single character alias for the option.</li> <li><code>default</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean[]></a> The default option value when it is not set by args. It must be of the same type as the <code>type</code> property. When <code>multiple</code> is <code>true</code>, it must be an array.</li> </ul> </li> <li><code>strict</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Should an error be thrown when unknown arguments are encountered, or when arguments are passed that do not match the <code>type</code> configured in <code>options</code>. <strong>Default:</strong> <code>true</code>.</li> <li><code>allowPositionals</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Whether this command accepts positional arguments. <strong>Default:</strong> <code>false</code> if <code>strict</code> is <code>true</code>, otherwise <code>true</code>.</li> <li><code>tokens</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Return the parsed tokens. This is useful for extending the built-in behavior, from adding additional checks through to reprocessing the tokens in different ways. <strong>Default:</strong> <code>false</code>.</li> </ul> </li> <li> <p>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The parsed command line arguments:</p> <ul> <li><code>values</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> A mapping of parsed option names with their <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> or <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> values.</li> <li><code>positionals</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> Positional arguments.</li> <li><code>tokens</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object[]></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> See <a href="#parseargs-tokens">parseArgs tokens</a> section. Only returned if <code>config</code> includes <code>tokens: true</code>.</li> </ul> </li> </ul> <p>Provides a higher level API for command-line argument parsing than interacting with <code>process.argv</code> directly. Takes a specification for the expected arguments and returns a structured object with the parsed options and positionals.</p> <pre class="with-43-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { parseArgs } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>; <span class="hljs-keyword">const</span> args = [<span class="hljs-string">'-f'</span>, <span class="hljs-string">'--bar'</span>, <span class="hljs-string">'b'</span>]; <span class="hljs-keyword">const</span> options = { <span class="hljs-attr">foo</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span>, <span class="hljs-attr">short</span>: <span class="hljs-string">'f'</span> }, <span class="hljs-attr">bar</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'string'</span> } }; <span class="hljs-keyword">const</span> { values, positionals } = <span class="hljs-title function_">parseArgs</span>({ args, options }); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(values, positionals); <span class="hljs-comment">// Prints: [Object: null prototype] { foo: true, bar: 'b' } []</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { parseArgs } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> args = [<span class="hljs-string">'-f'</span>, <span class="hljs-string">'--bar'</span>, <span class="hljs-string">'b'</span>]; <span class="hljs-keyword">const</span> options = { <span class="hljs-attr">foo</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span>, <span class="hljs-attr">short</span>: <span class="hljs-string">'f'</span> }, <span class="hljs-attr">bar</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'string'</span> } }; <span class="hljs-keyword">const</span> { values, positionals } = <span class="hljs-title function_">parseArgs</span>({ args, options }); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(values, positionals); <span class="hljs-comment">// Prints: [Object: null prototype] { foo: true, bar: 'b' } []</span></code></pre> <p><code>util.parseArgs</code> is experimental and behavior may change. Join the conversation in <a href="https://github.com/pkgjs/parseargs">pkgjs/parseargs</a> to contribute to the design.</p> <h4><code>parseArgs</code> <code>tokens</code><span><a class="mark" href="#parseargs-tokens" id="parseargs-tokens">#</a></span><a aria-hidden="true" class="legacy" id="util_parseargs_tokens"></a></h4> <p>Detailed parse information is available for adding custom behaviours by specifying <code>tokens: true</code> in the configuration. The returned tokens have properties describing:</p> <ul> <li>all tokens <ul> <li><code>kind</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> One of 'option', 'positional', or 'option-terminator'.</li> <li><code>index</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Index of element in <code>args</code> containing token. So the source argument for a token is <code>args[token.index]</code>.</li> </ul> </li> <li>option tokens <ul> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Long name of option.</li> <li><code>rawName</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> How option used in args, like <code>-f</code> of <code>--foo</code>.</li> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> Option value specified in args. Undefined for boolean options.</li> <li><code>inlineValue</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> Whether option value specified inline, like <code>--foo=bar</code>.</li> </ul> </li> <li>positional tokens <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The value of the positional argument in args (i.e. <code>args[index]</code>).</li> </ul> </li> <li>option-terminator token</li> </ul> <p>The returned tokens are in the order encountered in the input args. Options that appear more than once in args produce a token for each use. Short option groups like <code>-xy</code> expand to a token for each option. So <code>-xxx</code> produces three tokens.</p> <p>For example to use the returned tokens to add support for a negated option like <code>--no-color</code>, the tokens can be reprocessed to change the value stored for the negated option.</p> <pre class="with-43-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { parseArgs } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>; <span class="hljs-keyword">const</span> options = { <span class="hljs-string">'color'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span> }, <span class="hljs-string">'no-color'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span> }, <span class="hljs-string">'logfile'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'string'</span> }, <span class="hljs-string">'no-logfile'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span> }, }; <span class="hljs-keyword">const</span> { values, tokens } = <span class="hljs-title function_">parseArgs</span>({ options, <span class="hljs-attr">tokens</span>: <span class="hljs-literal">true</span> }); <span class="hljs-comment">// Reprocess the option tokens and overwrite the returned values.</span> tokens .<span class="hljs-title function_">filter</span>(<span class="hljs-function">(<span class="hljs-params">token</span>) =></span> token.<span class="hljs-property">kind</span> === <span class="hljs-string">'option'</span>) .<span class="hljs-title function_">forEach</span>(<span class="hljs-function">(<span class="hljs-params">token</span>) =></span> { <span class="hljs-keyword">if</span> (token.<span class="hljs-property">name</span>.<span class="hljs-title function_">startsWith</span>(<span class="hljs-string">'no-'</span>)) { <span class="hljs-comment">// Store foo:false for --no-foo</span> <span class="hljs-keyword">const</span> positiveName = token.<span class="hljs-property">name</span>.<span class="hljs-title function_">slice</span>(<span class="hljs-number">3</span>); values[positiveName] = <span class="hljs-literal">false</span>; <span class="hljs-keyword">delete</span> values[token.<span class="hljs-property">name</span>]; } <span class="hljs-keyword">else</span> { <span class="hljs-comment">// Resave value so last one wins if both --foo and --no-foo.</span> values[token.<span class="hljs-property">name</span>] = token.<span class="hljs-property">value</span> ?? <span class="hljs-literal">true</span>; } }); <span class="hljs-keyword">const</span> color = values.<span class="hljs-property">color</span>; <span class="hljs-keyword">const</span> logfile = values.<span class="hljs-property">logfile</span> ?? <span class="hljs-string">'default.log'</span>; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>({ logfile, color });</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { parseArgs } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> options = { <span class="hljs-string">'color'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span> }, <span class="hljs-string">'no-color'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span> }, <span class="hljs-string">'logfile'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'string'</span> }, <span class="hljs-string">'no-logfile'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span> }, }; <span class="hljs-keyword">const</span> { values, tokens } = <span class="hljs-title function_">parseArgs</span>({ options, <span class="hljs-attr">tokens</span>: <span class="hljs-literal">true</span> }); <span class="hljs-comment">// Reprocess the option tokens and overwrite the returned values.</span> tokens .<span class="hljs-title function_">filter</span>(<span class="hljs-function">(<span class="hljs-params">token</span>) =></span> token.<span class="hljs-property">kind</span> === <span class="hljs-string">'option'</span>) .<span class="hljs-title function_">forEach</span>(<span class="hljs-function">(<span class="hljs-params">token</span>) =></span> { <span class="hljs-keyword">if</span> (token.<span class="hljs-property">name</span>.<span class="hljs-title function_">startsWith</span>(<span class="hljs-string">'no-'</span>)) { <span class="hljs-comment">// Store foo:false for --no-foo</span> <span class="hljs-keyword">const</span> positiveName = token.<span class="hljs-property">name</span>.<span class="hljs-title function_">slice</span>(<span class="hljs-number">3</span>); values[positiveName] = <span class="hljs-literal">false</span>; <span class="hljs-keyword">delete</span> values[token.<span class="hljs-property">name</span>]; } <span class="hljs-keyword">else</span> { <span class="hljs-comment">// Resave value so last one wins if both --foo and --no-foo.</span> values[token.<span class="hljs-property">name</span>] = token.<span class="hljs-property">value</span> ?? <span class="hljs-literal">true</span>; } }); <span class="hljs-keyword">const</span> color = values.<span class="hljs-property">color</span>; <span class="hljs-keyword">const</span> logfile = values.<span class="hljs-property">logfile</span> ?? <span class="hljs-string">'default.log'</span>; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>({ logfile, color });</code></pre> <p>Example usage showing negated options, and when an option is used multiple ways then last one wins.</p> <pre><code class="language-console"><span class="hljs-meta prompt_">$ </span><span class="language-bash">node negate.js</span> { logfile: 'default.log', color: undefined } <span class="hljs-meta prompt_">$ </span><span class="language-bash">node negate.js --no-logfile --no-color</span> { logfile: false, color: false } <span class="hljs-meta prompt_">$ </span><span class="language-bash">node negate.js --logfile=test.log --color</span> { logfile: 'test.log', color: true } <span class="hljs-meta prompt_">$ </span><span class="language-bash">node negate.js --no-logfile --logfile=test.log --color --no-color</span> { logfile: 'test.log', color: false }</code></pre> </section><section><h3><code>util.promisify(original)</code><span><a class="mark" href="#utilpromisifyoriginal" id="utilpromisifyoriginal">#</a></span><a aria-hidden="true" class="legacy" id="util_util_promisify_original"></a></h3> <div class="api_metadata"> <span>Added in: v8.0.0</span> </div> <ul> <li><code>original</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> </ul> <p>Takes a function following the common error-first callback style, i.e. taking an <code>(err, value) => ...</code> callback as the last argument, and returns a version that returns promises.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>); <span class="hljs-keyword">const</span> stat = util.<span class="hljs-title function_">promisify</span>(fs.<span class="hljs-property">stat</span>); <span class="hljs-title function_">stat</span>(<span class="hljs-string">'.'</span>).<span class="hljs-title function_">then</span>(<span class="hljs-function">(<span class="hljs-params">stats</span>) =></span> { <span class="hljs-comment">// Do something with `stats`</span> }).<span class="hljs-title function_">catch</span>(<span class="hljs-function">(<span class="hljs-params">error</span>) =></span> { <span class="hljs-comment">// Handle the error.</span> });</code></pre> <p>Or, equivalently using <code>async function</code>s:</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>); <span class="hljs-keyword">const</span> stat = util.<span class="hljs-title function_">promisify</span>(fs.<span class="hljs-property">stat</span>); <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">callStat</span>(<span class="hljs-params"></span>) { <span class="hljs-keyword">const</span> stats = <span class="hljs-keyword">await</span> <span class="hljs-title function_">stat</span>(<span class="hljs-string">'.'</span>); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`This directory is owned by <span class="hljs-subst">${stats.uid}</span>`</span>); }</code></pre> <p>If there is an <code>original[util.promisify.custom]</code> property present, <code>promisify</code> will return its value, see <a href="#custom-promisified-functions">Custom promisified functions</a>.</p> <p><code>promisify()</code> assumes that <code>original</code> is a function taking a callback as its final argument in all cases. If <code>original</code> is not a function, <code>promisify()</code> will throw an error. If <code>original</code> is a function but its last argument is not an error-first callback, it will still be passed an error-first callback as its last argument.</p> <p>Using <code>promisify()</code> on class methods or other methods that use <code>this</code> may not work as expected unless handled specially:</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">class</span> <span class="hljs-title class_">Foo</span> { <span class="hljs-title function_">constructor</span>(<span class="hljs-params"></span>) { <span class="hljs-variable language_">this</span>.<span class="hljs-property">a</span> = <span class="hljs-number">42</span>; } <span class="hljs-title function_">bar</span>(<span class="hljs-params">callback</span>) { <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-variable language_">this</span>.<span class="hljs-property">a</span>); } } <span class="hljs-keyword">const</span> foo = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Foo</span>(); <span class="hljs-keyword">const</span> naiveBar = util.<span class="hljs-title function_">promisify</span>(foo.<span class="hljs-property">bar</span>); <span class="hljs-comment">// TypeError: Cannot read property 'a' of undefined</span> <span class="hljs-comment">// naiveBar().then(a => console.log(a));</span> naiveBar.<span class="hljs-title function_">call</span>(foo).<span class="hljs-title function_">then</span>(<span class="hljs-function">(<span class="hljs-params">a</span>) =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(a)); <span class="hljs-comment">// '42'</span> <span class="hljs-keyword">const</span> bindBar = naiveBar.<span class="hljs-title function_">bind</span>(foo); <span class="hljs-title function_">bindBar</span>().<span class="hljs-title function_">then</span>(<span class="hljs-function">(<span class="hljs-params">a</span>) =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(a)); <span class="hljs-comment">// '42'</span></code></pre> <h4>Custom promisified functions<span><a class="mark" href="#custom-promisified-functions" id="custom-promisified-functions">#</a></span><a aria-hidden="true" class="legacy" id="util_custom_promisified_functions"></a></h4> <p>Using the <code>util.promisify.custom</code> symbol one can override the return value of <a href="#utilpromisifyoriginal"><code>util.promisify()</code></a>:</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">function</span> <span class="hljs-title function_">doSomething</span>(<span class="hljs-params">foo, callback</span>) { <span class="hljs-comment">// ...</span> } doSomething[util.<span class="hljs-property">promisify</span>.<span class="hljs-property">custom</span>] = <span class="hljs-function">(<span class="hljs-params">foo</span>) =></span> { <span class="hljs-keyword">return</span> <span class="hljs-title function_">getPromiseSomehow</span>(); }; <span class="hljs-keyword">const</span> promisified = util.<span class="hljs-title function_">promisify</span>(doSomething); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(promisified === doSomething[util.<span class="hljs-property">promisify</span>.<span class="hljs-property">custom</span>]); <span class="hljs-comment">// prints 'true'</span></code></pre> <p>This can be useful for cases where the original function does not follow the standard format of taking an error-first callback as the last argument.</p> <p>For example, with a function that takes in <code>(foo, onSuccessCallback, onErrorCallback)</code>:</p> <pre><code class="language-js">doSomething[util.<span class="hljs-property">promisify</span>.<span class="hljs-property">custom</span>] = <span class="hljs-function">(<span class="hljs-params">foo</span>) =></span> { <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Promise</span>(<span class="hljs-function">(<span class="hljs-params">resolve, reject</span>) =></span> { <span class="hljs-title function_">doSomething</span>(foo, resolve, reject); }); };</code></pre> <p>If <code>promisify.custom</code> is defined but is not a function, <code>promisify()</code> will throw an error.</p> <h4><code>util.promisify.custom</code><span><a class="mark" href="#utilpromisifycustom" id="utilpromisifycustom">#</a></span><a aria-hidden="true" class="legacy" id="util_util_promisify_custom"></a></h4> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v13.12.0, v12.16.2</td> <td><p>This is now defined as a shared symbol.</p></td></tr> <tr><td>v8.0.0</td> <td><p><span>Added in: v8.0.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type" class="type"><symbol></a> that can be used to declare custom promisified variants of functions, see <a href="#custom-promisified-functions">Custom promisified functions</a>.</li> </ul> <p>In addition to being accessible through <code>util.promisify.custom</code>, this symbol is <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/for">registered globally</a> and can be accessed in any environment as <code>Symbol.for('nodejs.util.promisify.custom')</code>.</p> <p>For example, with a function that takes in <code>(foo, onSuccessCallback, onErrorCallback)</code>:</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> kCustomPromisifiedSymbol = <span class="hljs-title class_">Symbol</span>.<span class="hljs-title function_">for</span>(<span class="hljs-string">'nodejs.util.promisify.custom'</span>); doSomething[kCustomPromisifiedSymbol] = <span class="hljs-function">(<span class="hljs-params">foo</span>) =></span> { <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Promise</span>(<span class="hljs-function">(<span class="hljs-params">resolve, reject</span>) =></span> { <span class="hljs-title function_">doSomething</span>(foo, resolve, reject); }); };</code></pre> </section><section><h3><code>util.stripVTControlCharacters(str)</code><span><a class="mark" href="#utilstripvtcontrolcharactersstr" id="utilstripvtcontrolcharactersstr">#</a></span><a aria-hidden="true" class="legacy" id="util_util_stripvtcontrolcharacters_str"></a></h3> <div class="api_metadata"> <span>Added in: v16.11.0</span> </div> <ul> <li><code>str</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>Returns <code>str</code> with any ANSI escape codes removed.</p> <pre><code class="language-js"><span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-title function_">stripVTControlCharacters</span>(<span class="hljs-string">'\u001B[4mvalue\u001B[0m'</span>)); <span class="hljs-comment">// Prints "value"</span></code></pre> </section><section><h3>Class: <code>util.TextDecoder</code><span><a class="mark" href="#class-utiltextdecoder" id="class-utiltextdecoder">#</a></span><a aria-hidden="true" class="legacy" id="util_class_util_textdecoder"></a></h3> <div class="api_metadata"> <span>Added in: v8.3.0</span> </div> <p>An implementation of the <a href="https://encoding.spec.whatwg.org/">WHATWG Encoding Standard</a> <code>TextDecoder</code> API.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> decoder = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TextDecoder</span>(); <span class="hljs-keyword">const</span> u8arr = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint8Array</span>([<span class="hljs-number">72</span>, <span class="hljs-number">101</span>, <span class="hljs-number">108</span>, <span class="hljs-number">108</span>, <span class="hljs-number">111</span>]); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(decoder.<span class="hljs-title function_">decode</span>(u8arr)); <span class="hljs-comment">// Hello</span></code></pre> <h4>WHATWG supported encodings<span><a class="mark" href="#whatwg-supported-encodings" id="whatwg-supported-encodings">#</a></span><a aria-hidden="true" class="legacy" id="util_whatwg_supported_encodings"></a></h4> <p>Per the <a href="https://encoding.spec.whatwg.org/">WHATWG Encoding Standard</a>, the encodings supported by the <code>TextDecoder</code> API are outlined in the tables below. For each encoding, one or more aliases may be used.</p> <p>Different Node.js build configurations support different sets of encodings. (see <a href="intl.html">Internationalization</a>)</p> <h5>Encodings supported by default (with full ICU data)<span><a class="mark" href="#encodings-supported-by-default-with-full-icu-data" id="encodings-supported-by-default-with-full-icu-data">#</a></span><a aria-hidden="true" class="legacy" id="util_encodings_supported_by_default_with_full_icu_data"></a></h5> <table><thead><tr><th>Encoding</th><th>Aliases</th></tr></thead><tbody><tr><td><code>'ibm866'</code></td><td><code>'866'</code>, <code>'cp866'</code>, <code>'csibm866'</code></td></tr><tr><td><code>'iso-8859-2'</code></td><td><code>'csisolatin2'</code>, <code>'iso-ir-101'</code>, <code>'iso8859-2'</code>, <code>'iso88592'</code>, <code>'iso_8859-2'</code>, <code>'iso_8859-2:1987'</code>, <code>'l2'</code>, <code>'latin2'</code></td></tr><tr><td><code>'iso-8859-3'</code></td><td><code>'csisolatin3'</code>, <code>'iso-ir-109'</code>, <code>'iso8859-3'</code>, <code>'iso88593'</code>, <code>'iso_8859-3'</code>, <code>'iso_8859-3:1988'</code>, <code>'l3'</code>, <code>'latin3'</code></td></tr><tr><td><code>'iso-8859-4'</code></td><td><code>'csisolatin4'</code>, <code>'iso-ir-110'</code>, <code>'iso8859-4'</code>, <code>'iso88594'</code>, <code>'iso_8859-4'</code>, <code>'iso_8859-4:1988'</code>, <code>'l4'</code>, <code>'latin4'</code></td></tr><tr><td><code>'iso-8859-5'</code></td><td><code>'csisolatincyrillic'</code>, <code>'cyrillic'</code>, <code>'iso-ir-144'</code>, <code>'iso8859-5'</code>, <code>'iso88595'</code>, <code>'iso_8859-5'</code>, <code>'iso_8859-5:1988'</code></td></tr><tr><td><code>'iso-8859-6'</code></td><td><code>'arabic'</code>, <code>'asmo-708'</code>, <code>'csiso88596e'</code>, <code>'csiso88596i'</code>, <code>'csisolatinarabic'</code>, <code>'ecma-114'</code>, <code>'iso-8859-6-e'</code>, <code>'iso-8859-6-i'</code>, <code>'iso-ir-127'</code>, <code>'iso8859-6'</code>, <code>'iso88596'</code>, <code>'iso_8859-6'</code>, <code>'iso_8859-6:1987'</code></td></tr><tr><td><code>'iso-8859-7'</code></td><td><code>'csisolatingreek'</code>, <code>'ecma-118'</code>, <code>'elot_928'</code>, <code>'greek'</code>, <code>'greek8'</code>, <code>'iso-ir-126'</code>, <code>'iso8859-7'</code>, <code>'iso88597'</code>, <code>'iso_8859-7'</code>, <code>'iso_8859-7:1987'</code>, <code>'sun_eu_greek'</code></td></tr><tr><td><code>'iso-8859-8'</code></td><td><code>'csiso88598e'</code>, <code>'csisolatinhebrew'</code>, <code>'hebrew'</code>, <code>'iso-8859-8-e'</code>, <code>'iso-ir-138'</code>, <code>'iso8859-8'</code>, <code>'iso88598'</code>, <code>'iso_8859-8'</code>, <code>'iso_8859-8:1988'</code>, <code>'visual'</code></td></tr><tr><td><code>'iso-8859-8-i'</code></td><td><code>'csiso88598i'</code>, <code>'logical'</code></td></tr><tr><td><code>'iso-8859-10'</code></td><td><code>'csisolatin6'</code>, <code>'iso-ir-157'</code>, <code>'iso8859-10'</code>, <code>'iso885910'</code>, <code>'l6'</code>, <code>'latin6'</code></td></tr><tr><td><code>'iso-8859-13'</code></td><td><code>'iso8859-13'</code>, <code>'iso885913'</code></td></tr><tr><td><code>'iso-8859-14'</code></td><td><code>'iso8859-14'</code>, <code>'iso885914'</code></td></tr><tr><td><code>'iso-8859-15'</code></td><td><code>'csisolatin9'</code>, <code>'iso8859-15'</code>, <code>'iso885915'</code>, <code>'iso_8859-15'</code>, <code>'l9'</code></td></tr><tr><td><code>'koi8-r'</code></td><td><code>'cskoi8r'</code>, <code>'koi'</code>, <code>'koi8'</code>, <code>'koi8_r'</code></td></tr><tr><td><code>'koi8-u'</code></td><td><code>'koi8-ru'</code></td></tr><tr><td><code>'macintosh'</code></td><td><code>'csmacintosh'</code>, <code>'mac'</code>, <code>'x-mac-roman'</code></td></tr><tr><td><code>'windows-874'</code></td><td><code>'dos-874'</code>, <code>'iso-8859-11'</code>, <code>'iso8859-11'</code>, <code>'iso885911'</code>, <code>'tis-620'</code></td></tr><tr><td><code>'windows-1250'</code></td><td><code>'cp1250'</code>, <code>'x-cp1250'</code></td></tr><tr><td><code>'windows-1251'</code></td><td><code>'cp1251'</code>, <code>'x-cp1251'</code></td></tr><tr><td><code>'windows-1252'</code></td><td><code>'ansi_x3.4-1968'</code>, <code>'ascii'</code>, <code>'cp1252'</code>, <code>'cp819'</code>, <code>'csisolatin1'</code>, <code>'ibm819'</code>, <code>'iso-8859-1'</code>, <code>'iso-ir-100'</code>, <code>'iso8859-1'</code>, <code>'iso88591'</code>, <code>'iso_8859-1'</code>, <code>'iso_8859-1:1987'</code>, <code>'l1'</code>, <code>'latin1'</code>, <code>'us-ascii'</code>, <code>'x-cp1252'</code></td></tr><tr><td><code>'windows-1253'</code></td><td><code>'cp1253'</code>, <code>'x-cp1253'</code></td></tr><tr><td><code>'windows-1254'</code></td><td><code>'cp1254'</code>, <code>'csisolatin5'</code>, <code>'iso-8859-9'</code>, <code>'iso-ir-148'</code>, <code>'iso8859-9'</code>, <code>'iso88599'</code>, <code>'iso_8859-9'</code>, <code>'iso_8859-9:1989'</code>, <code>'l5'</code>, <code>'latin5'</code>, <code>'x-cp1254'</code></td></tr><tr><td><code>'windows-1255'</code></td><td><code>'cp1255'</code>, <code>'x-cp1255'</code></td></tr><tr><td><code>'windows-1256'</code></td><td><code>'cp1256'</code>, <code>'x-cp1256'</code></td></tr><tr><td><code>'windows-1257'</code></td><td><code>'cp1257'</code>, <code>'x-cp1257'</code></td></tr><tr><td><code>'windows-1258'</code></td><td><code>'cp1258'</code>, <code>'x-cp1258'</code></td></tr><tr><td><code>'x-mac-cyrillic'</code></td><td><code>'x-mac-ukrainian'</code></td></tr><tr><td><code>'gbk'</code></td><td><code>'chinese'</code>, <code>'csgb2312'</code>, <code>'csiso58gb231280'</code>, <code>'gb2312'</code>, <code>'gb_2312'</code>, <code>'gb_2312-80'</code>, <code>'iso-ir-58'</code>, <code>'x-gbk'</code></td></tr><tr><td><code>'gb18030'</code></td><td></td></tr><tr><td><code>'big5'</code></td><td><code>'big5-hkscs'</code>, <code>'cn-big5'</code>, <code>'csbig5'</code>, <code>'x-x-big5'</code></td></tr><tr><td><code>'euc-jp'</code></td><td><code>'cseucpkdfmtjapanese'</code>, <code>'x-euc-jp'</code></td></tr><tr><td><code>'iso-2022-jp'</code></td><td><code>'csiso2022jp'</code></td></tr><tr><td><code>'shift_jis'</code></td><td><code>'csshiftjis'</code>, <code>'ms932'</code>, <code>'ms_kanji'</code>, <code>'shift-jis'</code>, <code>'sjis'</code>, <code>'windows-31j'</code>, <code>'x-sjis'</code></td></tr><tr><td><code>'euc-kr'</code></td><td><code>'cseuckr'</code>, <code>'csksc56011987'</code>, <code>'iso-ir-149'</code>, <code>'korean'</code>, <code>'ks_c_5601-1987'</code>, <code>'ks_c_5601-1989'</code>, <code>'ksc5601'</code>, <code>'ksc_5601'</code>, <code>'windows-949'</code></td></tr></tbody></table> <h5>Encodings supported when Node.js is built with the <code>small-icu</code> option<span><a class="mark" href="#encodings-supported-when-nodejs-is-built-with-the-small-icu-option" id="encodings-supported-when-nodejs-is-built-with-the-small-icu-option">#</a></span><a aria-hidden="true" class="legacy" id="util_encodings_supported_when_node_js_is_built_with_the_small_icu_option"></a></h5> <table><thead><tr><th>Encoding</th><th>Aliases</th></tr></thead><tbody><tr><td><code>'utf-8'</code></td><td><code>'unicode-1-1-utf-8'</code>, <code>'utf8'</code></td></tr><tr><td><code>'utf-16le'</code></td><td><code>'utf-16'</code></td></tr><tr><td><code>'utf-16be'</code></td><td></td></tr></tbody></table> <h5>Encodings supported when ICU is disabled<span><a class="mark" href="#encodings-supported-when-icu-is-disabled" id="encodings-supported-when-icu-is-disabled">#</a></span><a aria-hidden="true" class="legacy" id="util_encodings_supported_when_icu_is_disabled"></a></h5> <table><thead><tr><th>Encoding</th><th>Aliases</th></tr></thead><tbody><tr><td><code>'utf-8'</code></td><td><code>'unicode-1-1-utf-8'</code>, <code>'utf8'</code></td></tr><tr><td><code>'utf-16le'</code></td><td><code>'utf-16'</code></td></tr></tbody></table> <p>The <code>'iso-8859-16'</code> encoding listed in the <a href="https://encoding.spec.whatwg.org/">WHATWG Encoding Standard</a> is not supported.</p> <h4><code>new TextDecoder([encoding[, options]])</code><span><a class="mark" href="#new-textdecoderencoding-options" id="new-textdecoderencoding-options">#</a></span><a aria-hidden="true" class="legacy" id="util_new_textdecoder_encoding_options"></a></h4> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v11.0.0</td> <td><p>The class is now available on the global object.</p></td></tr> <tr><td>v8.3.0</td> <td><p><span>Added in: v8.3.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Identifies the <code>encoding</code> that this <code>TextDecoder</code> instance supports. <strong>Default:</strong> <code>'utf-8'</code>.</li> <li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> <ul> <li><code>fatal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> if decoding failures are fatal. This option is not supported when ICU is disabled (see <a href="intl.html">Internationalization</a>). <strong>Default:</strong> <code>false</code>.</li> <li><code>ignoreBOM</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, the <code>TextDecoder</code> will include the byte order mark in the decoded result. When <code>false</code>, the byte order mark will be removed from the output. This option is only used when <code>encoding</code> is <code>'utf-8'</code>, <code>'utf-16be'</code>, or <code>'utf-16le'</code>. <strong>Default:</strong> <code>false</code>.</li> </ul> </li> </ul> <p>Creates a new <code>TextDecoder</code> instance. The <code>encoding</code> may specify one of the supported encodings or an alias.</p> <p>The <code>TextDecoder</code> class is also available on the global object.</p> <h4><code>textDecoder.decode([input[, options]])</code><span><a class="mark" href="#textdecoderdecodeinput-options" id="textdecoderdecodeinput-options">#</a></span><a aria-hidden="true" class="legacy" id="util_textdecoder_decode_input_options"></a></h4> <ul> <li><code>input</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer" class="type"><ArrayBuffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> An <code>ArrayBuffer</code>, <code>DataView</code>, or <code>TypedArray</code> instance containing the encoded data.</li> <li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> <ul> <li><code>stream</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> if additional chunks of data are expected. <strong>Default:</strong> <code>false</code>.</li> </ul> </li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>Decodes the <code>input</code> and returns a string. If <code>options.stream</code> is <code>true</code>, any incomplete byte sequences occurring at the end of the <code>input</code> are buffered internally and emitted after the next call to <code>textDecoder.decode()</code>.</p> <p>If <code>textDecoder.fatal</code> is <code>true</code>, decoding errors that occur will result in a <code>TypeError</code> being thrown.</p> <h4><code>textDecoder.encoding</code><span><a class="mark" href="#textdecoderencoding" id="textdecoderencoding">#</a></span><a aria-hidden="true" class="legacy" id="util_textdecoder_encoding"></a></h4> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>The encoding supported by the <code>TextDecoder</code> instance.</p> <h4><code>textDecoder.fatal</code><span><a class="mark" href="#textdecoderfatal" id="textdecoderfatal">#</a></span><a aria-hidden="true" class="legacy" id="util_textdecoder_fatal"></a></h4> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>The value will be <code>true</code> if decoding errors result in a <code>TypeError</code> being thrown.</p> <h4><code>textDecoder.ignoreBOM</code><span><a class="mark" href="#textdecoderignorebom" id="textdecoderignorebom">#</a></span><a aria-hidden="true" class="legacy" id="util_textdecoder_ignorebom"></a></h4> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>The value will be <code>true</code> if the decoding result will include the byte order mark.</p> </section><section><h3>Class: <code>util.TextEncoder</code><span><a class="mark" href="#class-utiltextencoder" id="class-utiltextencoder">#</a></span><a aria-hidden="true" class="legacy" id="util_class_util_textencoder"></a></h3> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v11.0.0</td> <td><p>The class is now available on the global object.</p></td></tr> <tr><td>v8.3.0</td> <td><p><span>Added in: v8.3.0</span></p></td></tr> </tbody></table> </details> </div> <p>An implementation of the <a href="https://encoding.spec.whatwg.org/">WHATWG Encoding Standard</a> <code>TextEncoder</code> API. All instances of <code>TextEncoder</code> only support UTF-8 encoding.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> encoder = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TextEncoder</span>(); <span class="hljs-keyword">const</span> uint8array = encoder.<span class="hljs-title function_">encode</span>(<span class="hljs-string">'this is some data'</span>);</code></pre> <p>The <code>TextEncoder</code> class is also available on the global object.</p> <h4><code>textEncoder.encode([input])</code><span><a class="mark" href="#textencoderencodeinput" id="textencoderencodeinput">#</a></span><a aria-hidden="true" class="legacy" id="util_textencoder_encode_input"></a></h4> <ul> <li><code>input</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The text to encode. <strong>Default:</strong> an empty string.</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array" class="type"><Uint8Array></a></li> </ul> <p>UTF-8 encodes the <code>input</code> string and returns a <code>Uint8Array</code> containing the encoded bytes.</p> <h4><code>textEncoder.encodeInto(src, dest)</code><span><a class="mark" href="#textencoderencodeintosrc-dest" id="textencoderencodeintosrc-dest">#</a></span><a aria-hidden="true" class="legacy" id="util_textencoder_encodeinto_src_dest"></a></h4> <ul> <li><code>src</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The text to encode.</li> <li><code>dest</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array" class="type"><Uint8Array></a> The array to hold the encode result.</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> <ul> <li><code>read</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The read Unicode code units of src.</li> <li><code>written</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The written UTF-8 bytes of dest.</li> </ul> </li> </ul> <p>UTF-8 encodes the <code>src</code> string to the <code>dest</code> Uint8Array and returns an object containing the read Unicode code units and written UTF-8 bytes.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> encoder = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TextEncoder</span>(); <span class="hljs-keyword">const</span> src = <span class="hljs-string">'this is some data'</span>; <span class="hljs-keyword">const</span> dest = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint8Array</span>(<span class="hljs-number">10</span>); <span class="hljs-keyword">const</span> { read, written } = encoder.<span class="hljs-title function_">encodeInto</span>(src, dest);</code></pre> <h4><code>textEncoder.encoding</code><span><a class="mark" href="#textencoderencoding" id="textencoderencoding">#</a></span><a aria-hidden="true" class="legacy" id="util_textencoder_encoding"></a></h4> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>The encoding supported by the <code>TextEncoder</code> instance. Always set to <code>'utf-8'</code>.</p> </section><section><h3><code>util.toUSVString(string)</code><span><a class="mark" href="#utiltousvstringstring" id="utiltousvstringstring">#</a></span><a aria-hidden="true" class="legacy" id="util_util_tousvstring_string"></a></h3> <div class="api_metadata"> <span>Added in: v16.8.0</span> </div> <ul> <li><code>string</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>Returns the <code>string</code> after replacing any surrogate code points (or equivalently, any unpaired surrogate code units) with the Unicode "replacement character" U+FFFD.</p> </section><section><h3><code>util.types</code><span><a class="mark" href="#utiltypes" id="utiltypes">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types"></a></h3> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v15.3.0</td> <td><p>Exposed as <code>require('util/types')</code>.</p></td></tr> <tr><td>v10.0.0</td> <td><p><span>Added in: v10.0.0</span></p></td></tr> </tbody></table> </details> </div> <p><code>util.types</code> provides type checks for different kinds of built-in objects. Unlike <code>instanceof</code> or <code>Object.prototype.toString.call(value)</code>, these checks do not inspect properties of the object that are accessible from JavaScript (like their prototype), and usually have the overhead of calling into C++.</p> <p>The result generally does not make any guarantees about what kinds of properties or behavior a value exposes in JavaScript. They are primarily useful for addon developers who prefer to do type checking in JavaScript.</p> <p>The API is accessible via <code>require('node:util').types</code> or <code>require('node:util/types')</code>.</p> <h4><code>util.types.isAnyArrayBuffer(value)</code><span><a class="mark" href="#utiltypesisanyarraybuffervalue" id="utiltypesisanyarraybuffervalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isanyarraybuffer_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a> or <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer"><code>SharedArrayBuffer</code></a> instance.</p> <p>See also <a href="#utiltypesisarraybuffervalue"><code>util.types.isArrayBuffer()</code></a> and <a href="#utiltypesissharedarraybuffervalue"><code>util.types.isSharedArrayBuffer()</code></a>.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isAnyArrayBuffer</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isAnyArrayBuffer</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">SharedArrayBuffer</span>()); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isArrayBufferView(value)</code><span><a class="mark" href="#utiltypesisarraybufferviewvalue" id="utiltypesisarraybufferviewvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isarraybufferview_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is an instance of one of the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a> views, such as typed array objects or <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView"><code>DataView</code></a>. Equivalent to <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView"><code>ArrayBuffer.isView()</code></a>.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArrayBufferView</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Int8Array</span>()); <span class="hljs-comment">// true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArrayBufferView</span>(<span class="hljs-title class_">Buffer</span>.<span class="hljs-title function_">from</span>(<span class="hljs-string">'hello world'</span>)); <span class="hljs-comment">// true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArrayBufferView</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">DataView</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>(<span class="hljs-number">16</span>))); <span class="hljs-comment">// true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArrayBufferView</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// false</span></code></pre> <h4><code>util.types.isArgumentsObject(value)</code><span><a class="mark" href="#utiltypesisargumentsobjectvalue" id="utiltypesisargumentsobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isargumentsobject_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is an <code>arguments</code> object.</p> <!-- eslint-disable prefer-rest-params --> <pre><code class="language-js"><span class="hljs-keyword">function</span> <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) { util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArgumentsObject</span>(<span class="hljs-variable language_">arguments</span>); <span class="hljs-comment">// Returns true</span> }</code></pre> <h4><code>util.types.isArrayBuffer(value)</code><span><a class="mark" href="#utiltypesisarraybuffervalue" id="utiltypesisarraybuffervalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isarraybuffer_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a> instance. This does <em>not</em> include <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer"><code>SharedArrayBuffer</code></a> instances. Usually, it is desirable to test for both; See <a href="#utiltypesisanyarraybuffervalue"><code>util.types.isAnyArrayBuffer()</code></a> for that.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArrayBuffer</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArrayBuffer</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">SharedArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span></code></pre> <h4><code>util.types.isAsyncFunction(value)</code><span><a class="mark" href="#utiltypesisasyncfunctionvalue" id="utiltypesisasyncfunctionvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isasyncfunction_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function">async function</a>. This only reports back what the JavaScript engine is seeing; in particular, the return value may not match the original source code if a transpilation tool was used.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isAsyncFunction</span>(<span class="hljs-keyword">function</span> <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) {}); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isAsyncFunction</span>(<span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) {}); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isBigInt64Array(value)</code><span><a class="mark" href="#utiltypesisbigint64arrayvalue" id="utiltypesisbigint64arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isbigint64array_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a <code>BigInt64Array</code> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBigInt64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">BigInt64Array</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBigInt64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">BigUint64Array</span>()); <span class="hljs-comment">// Returns false</span></code></pre> <h4><code>util.types.isBigUint64Array(value)</code><span><a class="mark" href="#utiltypesisbiguint64arrayvalue" id="utiltypesisbiguint64arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isbiguint64array_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a <code>BigUint64Array</code> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBigUint64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">BigInt64Array</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBigUint64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">BigUint64Array</span>()); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isBooleanObject(value)</code><span><a class="mark" href="#utiltypesisbooleanobjectvalue" id="utiltypesisbooleanobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isbooleanobject_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a boolean object, e.g. created by <code>new Boolean()</code>.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBooleanObject</span>(<span class="hljs-literal">false</span>); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBooleanObject</span>(<span class="hljs-literal">true</span>); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBooleanObject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Boolean</span>(<span class="hljs-literal">false</span>)); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBooleanObject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Boolean</span>(<span class="hljs-literal">true</span>)); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBooleanObject</span>(<span class="hljs-title class_">Boolean</span>(<span class="hljs-literal">false</span>)); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBooleanObject</span>(<span class="hljs-title class_">Boolean</span>(<span class="hljs-literal">true</span>)); <span class="hljs-comment">// Returns false</span></code></pre> <h4><code>util.types.isBoxedPrimitive(value)</code><span><a class="mark" href="#utiltypesisboxedprimitivevalue" id="utiltypesisboxedprimitivevalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isboxedprimitive_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.11.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is any boxed primitive object, e.g. created by <code>new Boolean()</code>, <code>new String()</code> or <code>Object(Symbol())</code>.</p> <p>For example:</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBoxedPrimitive</span>(<span class="hljs-literal">false</span>); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBoxedPrimitive</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Boolean</span>(<span class="hljs-literal">false</span>)); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBoxedPrimitive</span>(<span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'foo'</span>)); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBoxedPrimitive</span>(<span class="hljs-title class_">Object</span>(<span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'foo'</span>))); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBoxedPrimitive</span>(<span class="hljs-title class_">Object</span>(<span class="hljs-title class_">BigInt</span>(<span class="hljs-number">5</span>))); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isCryptoKey(value)</code><span><a class="mark" href="#utiltypesiscryptokeyvalue" id="utiltypesiscryptokeyvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_iscryptokey_value"></a></h4> <div class="api_metadata"> <span>Added in: v16.2.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if <code>value</code> is a <a href="webcrypto.html#class-cryptokey" class="type"><CryptoKey></a>, <code>false</code> otherwise.</p> <h4><code>util.types.isDataView(value)</code><span><a class="mark" href="#utiltypesisdataviewvalue" id="utiltypesisdataviewvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isdataview_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView"><code>DataView</code></a> instance.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> ab = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>(<span class="hljs-number">20</span>); util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isDataView</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">DataView</span>(ab)); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isDataView</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code></pre> <p>See also <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView"><code>ArrayBuffer.isView()</code></a>.</p> <h4><code>util.types.isDate(value)</code><span><a class="mark" href="#utiltypesisdatevalue" id="utiltypesisdatevalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isdate_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date"><code>Date</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isDate</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>()); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isExternal(value)</code><span><a class="mark" href="#utiltypesisexternalvalue" id="utiltypesisexternalvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isexternal_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a native <code>External</code> value.</p> <p>A native <code>External</code> value is a special type of object that contains a raw C++ pointer (<code>void*</code>) for access from native code, and has no other properties. Such objects are created either by Node.js internals or native addons. In JavaScript, they are <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze">frozen</a> objects with a <code>null</code> prototype.</p> <pre><code class="language-c"><span class="hljs-meta">#<span class="hljs-keyword">include</span> <span class="hljs-string"><js_native_api.h></span></span> <span class="hljs-meta">#<span class="hljs-keyword">include</span> <span class="hljs-string"><stdlib.h></span></span> napi_value result; <span class="hljs-type">static</span> napi_value <span class="hljs-title function_">MyNapi</span><span class="hljs-params">(napi_env env, napi_callback_info info)</span> { <span class="hljs-type">int</span>* raw = (<span class="hljs-type">int</span>*) <span class="hljs-built_in">malloc</span>(<span class="hljs-number">1024</span>); napi_status status = napi_create_external(env, (<span class="hljs-type">void</span>*) raw, <span class="hljs-literal">NULL</span>, <span class="hljs-literal">NULL</span>, &result); <span class="hljs-keyword">if</span> (status != napi_ok) { napi_throw_error(env, <span class="hljs-literal">NULL</span>, <span class="hljs-string">"napi_create_external failed"</span>); <span class="hljs-keyword">return</span> <span class="hljs-literal">NULL</span>; } <span class="hljs-keyword">return</span> result; } ... DECLARE_NAPI_PROPERTY(<span class="hljs-string">"myNapi"</span>, MyNapi) ...</code></pre> <pre><code class="language-js"><span class="hljs-keyword">const</span> native = <span class="hljs-built_in">require</span>(<span class="hljs-string">'napi_addon.node'</span>); <span class="hljs-keyword">const</span> data = native.<span class="hljs-title function_">myNapi</span>(); util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isExternal</span>(data); <span class="hljs-comment">// returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isExternal</span>(<span class="hljs-number">0</span>); <span class="hljs-comment">// returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isExternal</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">String</span>(<span class="hljs-string">'foo'</span>)); <span class="hljs-comment">// returns false</span></code></pre> <p>For further information on <code>napi_create_external</code>, refer to <a href="n-api.html#napi_create_external"><code>napi_create_external()</code></a>.</p> <h4><code>util.types.isFloat32Array(value)</code><span><a class="mark" href="#utiltypesisfloat32arrayvalue" id="utiltypesisfloat32arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isfloat32array_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float32Array"><code>Float32Array</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isFloat32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isFloat32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float32Array</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isFloat32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code></pre> <h4><code>util.types.isFloat64Array(value)</code><span><a class="mark" href="#utiltypesisfloat64arrayvalue" id="utiltypesisfloat64arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isfloat64array_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float64Array"><code>Float64Array</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isFloat64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isFloat64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint8Array</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isFloat64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isGeneratorFunction(value)</code><span><a class="mark" href="#utiltypesisgeneratorfunctionvalue" id="utiltypesisgeneratorfunctionvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isgeneratorfunction_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a generator function. This only reports back what the JavaScript engine is seeing; in particular, the return value may not match the original source code if a transpilation tool was used.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isGeneratorFunction</span>(<span class="hljs-keyword">function</span> <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) {}); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isGeneratorFunction</span>(<span class="hljs-keyword">function</span>* <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) {}); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isGeneratorObject(value)</code><span><a class="mark" href="#utiltypesisgeneratorobjectvalue" id="utiltypesisgeneratorobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isgeneratorobject_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a generator object as returned from a built-in generator function. This only reports back what the JavaScript engine is seeing; in particular, the return value may not match the original source code if a transpilation tool was used.</p> <pre><code class="language-js"><span class="hljs-keyword">function</span>* <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) {} <span class="hljs-keyword">const</span> generator = <span class="hljs-title function_">foo</span>(); util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isGeneratorObject</span>(generator); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isInt8Array(value)</code><span><a class="mark" href="#utiltypesisint8arrayvalue" id="utiltypesisint8arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isint8array_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int8Array"><code>Int8Array</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt8Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt8Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Int8Array</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt8Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code></pre> <h4><code>util.types.isInt16Array(value)</code><span><a class="mark" href="#utiltypesisint16arrayvalue" id="utiltypesisint16arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isint16array_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int16Array"><code>Int16Array</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt16Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt16Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Int16Array</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt16Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code></pre> <h4><code>util.types.isInt32Array(value)</code><span><a class="mark" href="#utiltypesisint32arrayvalue" id="utiltypesisint32arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isint32array_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int32Array"><code>Int32Array</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Int32Array</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code></pre> <h4><code>util.types.isKeyObject(value)</code><span><a class="mark" href="#utiltypesiskeyobjectvalue" id="utiltypesiskeyobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_iskeyobject_value"></a></h4> <div class="api_metadata"> <span>Added in: v16.2.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if <code>value</code> is a <a href="crypto.html#class-keyobject" class="type"><KeyObject></a>, <code>false</code> otherwise.</p> <h4><code>util.types.isMap(value)</code><span><a class="mark" href="#utiltypesismapvalue" id="utiltypesismapvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_ismap_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isMap</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Map</span>()); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isMapIterator(value)</code><span><a class="mark" href="#utiltypesismapiteratorvalue" id="utiltypesismapiteratorvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_ismapiterator_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is an iterator returned for a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> instance.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> map = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Map</span>(); util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isMapIterator</span>(map.<span class="hljs-title function_">keys</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isMapIterator</span>(map.<span class="hljs-title function_">values</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isMapIterator</span>(map.<span class="hljs-title function_">entries</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isMapIterator</span>(map[<span class="hljs-title class_">Symbol</span>.<span class="hljs-property">iterator</span>]()); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isModuleNamespaceObject(value)</code><span><a class="mark" href="#utiltypesismodulenamespaceobjectvalue" id="utiltypesismodulenamespaceobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_ismodulenamespaceobject_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is an instance of a <a href="https://tc39.github.io/ecma262/#sec-module-namespace-exotic-objects">Module Namespace Object</a>.</p> <!-- eslint-skip --> <pre><code class="language-js"><span class="hljs-keyword">import</span> * <span class="hljs-keyword">as</span> ns <span class="hljs-keyword">from</span> <span class="hljs-string">'./a.js'</span>; util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isModuleNamespaceObject</span>(ns); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isNativeError(value)</code><span><a class="mark" href="#utiltypesisnativeerrorvalue" id="utiltypesisnativeerrorvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isnativeerror_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is an instance of a built-in <a href="errors.html#class-error"><code>Error</code></a> type.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNativeError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNativeError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNativeError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">RangeError</span>()); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isNumberObject(value)</code><span><a class="mark" href="#utiltypesisnumberobjectvalue" id="utiltypesisnumberobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isnumberobject_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a number object, e.g. created by <code>new Number()</code>.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNumberObject</span>(<span class="hljs-number">0</span>); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNumberObject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Number</span>(<span class="hljs-number">0</span>)); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isPromise(value)</code><span><a class="mark" href="#utiltypesispromisevalue" id="utiltypesispromisevalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_ispromise_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise"><code>Promise</code></a>.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isPromise</span>(<span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">resolve</span>(<span class="hljs-number">42</span>)); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isProxy(value)</code><span><a class="mark" href="#utiltypesisproxyvalue" id="utiltypesisproxyvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isproxy_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy"><code>Proxy</code></a> instance.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> target = {}; <span class="hljs-keyword">const</span> proxy = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Proxy</span>(target, {}); util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isProxy</span>(target); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isProxy</span>(proxy); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isRegExp(value)</code><span><a class="mark" href="#utiltypesisregexpvalue" id="utiltypesisregexpvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isregexp_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a regular expression object.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isRegExp</span>(<span class="hljs-regexp">/abc/</span>); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isRegExp</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">RegExp</span>(<span class="hljs-string">'abc'</span>)); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isSet(value)</code><span><a class="mark" href="#utiltypesissetvalue" id="utiltypesissetvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isset_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSet</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Set</span>()); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isSetIterator(value)</code><span><a class="mark" href="#utiltypesissetiteratorvalue" id="utiltypesissetiteratorvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_issetiterator_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is an iterator returned for a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> instance.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> set = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Set</span>(); util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSetIterator</span>(set.<span class="hljs-title function_">keys</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSetIterator</span>(set.<span class="hljs-title function_">values</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSetIterator</span>(set.<span class="hljs-title function_">entries</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSetIterator</span>(set[<span class="hljs-title class_">Symbol</span>.<span class="hljs-property">iterator</span>]()); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isSharedArrayBuffer(value)</code><span><a class="mark" href="#utiltypesissharedarraybuffervalue" id="utiltypesissharedarraybuffervalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_issharedarraybuffer_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer"><code>SharedArrayBuffer</code></a> instance. This does <em>not</em> include <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a> instances. Usually, it is desirable to test for both; See <a href="#utiltypesisanyarraybuffervalue"><code>util.types.isAnyArrayBuffer()</code></a> for that.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSharedArrayBuffer</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSharedArrayBuffer</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">SharedArrayBuffer</span>()); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isStringObject(value)</code><span><a class="mark" href="#utiltypesisstringobjectvalue" id="utiltypesisstringobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isstringobject_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a string object, e.g. created by <code>new String()</code>.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isStringObject</span>(<span class="hljs-string">'foo'</span>); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isStringObject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">String</span>(<span class="hljs-string">'foo'</span>)); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isSymbolObject(value)</code><span><a class="mark" href="#utiltypesissymbolobjectvalue" id="utiltypesissymbolobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_issymbolobject_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a symbol object, created by calling <code>Object()</code> on a <code>Symbol</code> primitive.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> symbol = <span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'foo'</span>); util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSymbolObject</span>(symbol); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSymbolObject</span>(<span class="hljs-title class_">Object</span>(symbol)); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isTypedArray(value)</code><span><a class="mark" href="#utiltypesistypedarrayvalue" id="utiltypesistypedarrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_istypedarray_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray"><code>TypedArray</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isTypedArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isTypedArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint8Array</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isTypedArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns true</span></code></pre> <p>See also <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView"><code>ArrayBuffer.isView()</code></a>.</p> <h4><code>util.types.isUint8Array(value)</code><span><a class="mark" href="#utiltypesisuint8arrayvalue" id="utiltypesisuint8arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isuint8array_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array"><code>Uint8Array</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint8Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint8Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint8Array</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint8Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code></pre> <h4><code>util.types.isUint8ClampedArray(value)</code><span><a class="mark" href="#utiltypesisuint8clampedarrayvalue" id="utiltypesisuint8clampedarrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isuint8clampedarray_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8ClampedArray"><code>Uint8ClampedArray</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint8ClampedArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint8ClampedArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint8ClampedArray</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint8ClampedArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code></pre> <h4><code>util.types.isUint16Array(value)</code><span><a class="mark" href="#utiltypesisuint16arrayvalue" id="utiltypesisuint16arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isuint16array_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint16Array"><code>Uint16Array</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint16Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint16Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint16Array</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint16Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code></pre> <h4><code>util.types.isUint32Array(value)</code><span><a class="mark" href="#utiltypesisuint32arrayvalue" id="utiltypesisuint32arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isuint32array_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint32Array"><code>Uint32Array</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint32Array</span>()); <span class="hljs-comment">// Returns true</span> util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code></pre> <h4><code>util.types.isWeakMap(value)</code><span><a class="mark" href="#utiltypesisweakmapvalue" id="utiltypesisweakmapvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isweakmap_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isWeakMap</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakMap</span>()); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isWeakSet(value)</code><span><a class="mark" href="#utiltypesisweaksetvalue" id="utiltypesisweaksetvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isweakset_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span> </div> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> instance.</p> <pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isWeakSet</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakSet</span>()); <span class="hljs-comment">// Returns true</span></code></pre> <h4><code>util.types.isWebAssemblyCompiledModule(value)</code><span><a class="mark" href="#utiltypesiswebassemblycompiledmodulevalue" id="utiltypesiswebassemblycompiledmodulevalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_iswebassemblycompiledmodule_value"></a></h4> <div class="api_metadata"> <span>Added in: v10.0.0</span><span>Deprecated since: v14.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>value instanceof WebAssembly.Module</code> instead.</div><p></p> <ul> <li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Module"><code>WebAssembly.Module</code></a> instance.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> <span class="hljs-variable language_">module</span> = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WebAssembly</span>.<span class="hljs-title class_">Module</span>(wasmBuffer); util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isWebAssemblyCompiledModule</span>(<span class="hljs-variable language_">module</span>); <span class="hljs-comment">// Returns true</span></code></pre> </section><section><h3>Deprecated APIs<span><a class="mark" href="#deprecated-apis" id="deprecated-apis">#</a></span><a aria-hidden="true" class="legacy" id="util_deprecated_apis"></a></h3> <p>The following APIs are deprecated and should no longer be used. Existing applications and modules should be updated to find alternative approaches.</p> <h4><code>util._extend(target, source)</code><span><a class="mark" href="#util_extendtarget-source" id="util_extendtarget-source">#</a></span><a aria-hidden="true" class="legacy" id="util_util_extend_target_source"></a></h4> <div class="api_metadata"> <span>Added in: v0.7.5</span><span>Deprecated since: v6.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign"><code>Object.assign()</code></a> instead.</div><p></p> <ul> <li><code>target</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> <li><code>source</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> </ul> <p>The <code>util._extend()</code> method was never intended to be used outside of internal Node.js modules. The community found and used it anyway.</p> <p>It is deprecated and should not be used in new code. JavaScript comes with very similar built-in functionality through <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign"><code>Object.assign()</code></a>.</p> <h4><code>util.isArray(object)</code><span><a class="mark" href="#utilisarrayobject" id="utilisarrayobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isarray_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.6.0</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray"><code>Array.isArray()</code></a> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Alias for <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray"><code>Array.isArray()</code></a>.</p> <p>Returns <code>true</code> if the given <code>object</code> is an <code>Array</code>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isArray</span>([]); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Array</span>()); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isArray</span>({}); <span class="hljs-comment">// Returns: false</span></code></pre> <h4><code>util.isBoolean(object)</code><span><a class="mark" href="#utilisbooleanobject" id="utilisbooleanobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isboolean_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'boolean'</code> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is a <code>Boolean</code>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isBoolean</span>(<span class="hljs-number">1</span>); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isBoolean</span>(<span class="hljs-number">0</span>); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isBoolean</span>(<span class="hljs-literal">false</span>); <span class="hljs-comment">// Returns: true</span></code></pre> <h4><code>util.isBuffer(object)</code><span><a class="mark" href="#utilisbufferobject" id="utilisbufferobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isbuffer_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <a href="buffer.html#static-method-bufferisbufferobj"><code>Buffer.isBuffer()</code></a> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is a <code>Buffer</code>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isBuffer</span>({ <span class="hljs-attr">length</span>: <span class="hljs-number">0</span> }); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isBuffer</span>([]); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isBuffer</span>(<span class="hljs-title class_">Buffer</span>.<span class="hljs-title function_">from</span>(<span class="hljs-string">'hello world'</span>)); <span class="hljs-comment">// Returns: true</span></code></pre> <h4><code>util.isDate(object)</code><span><a class="mark" href="#utilisdateobject" id="utilisdateobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isdate_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.6.0</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <a href="#utiltypesisdatevalue"><code>util.types.isDate()</code></a> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is a <code>Date</code>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isDate</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>()); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isDate</span>(<span class="hljs-title class_">Date</span>()); <span class="hljs-comment">// false (without 'new' returns a String)</span> util.<span class="hljs-title function_">isDate</span>({}); <span class="hljs-comment">// Returns: false</span></code></pre> <h4><code>util.isError(object)</code><span><a class="mark" href="#utiliserrorobject" id="utiliserrorobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_iserror_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.6.0</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <a href="#utiltypesisnativeerrorvalue"><code>util.types.isNativeError()</code></a> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is an <a href="errors.html#class-error"><code>Error</code></a>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>()); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>()); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isError</span>({ <span class="hljs-attr">name</span>: <span class="hljs-string">'Error'</span>, <span class="hljs-attr">message</span>: <span class="hljs-string">'an error occurred'</span> }); <span class="hljs-comment">// Returns: false</span></code></pre> <p>This method relies on <code>Object.prototype.toString()</code> behavior. It is possible to obtain an incorrect result when the <code>object</code> argument manipulates <code>@@toStringTag</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> obj = { <span class="hljs-attr">name</span>: <span class="hljs-string">'Error'</span>, <span class="hljs-attr">message</span>: <span class="hljs-string">'an error occurred'</span> }; util.<span class="hljs-title function_">isError</span>(obj); <span class="hljs-comment">// Returns: false</span> obj[<span class="hljs-title class_">Symbol</span>.<span class="hljs-property">toStringTag</span>] = <span class="hljs-string">'Error'</span>; util.<span class="hljs-title function_">isError</span>(obj); <span class="hljs-comment">// Returns: true</span></code></pre> <h4><code>util.isFunction(object)</code><span><a class="mark" href="#utilisfunctionobject" id="utilisfunctionobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isfunction_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'function'</code> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is a <code>Function</code>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">function</span> <span class="hljs-title function_">Foo</span>(<span class="hljs-params"></span>) {} <span class="hljs-keyword">const</span> <span class="hljs-title function_">Bar</span> = (<span class="hljs-params"></span>) => {}; util.<span class="hljs-title function_">isFunction</span>({}); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isFunction</span>(<span class="hljs-title class_">Foo</span>); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isFunction</span>(<span class="hljs-title class_">Bar</span>); <span class="hljs-comment">// Returns: true</span></code></pre> <h4><code>util.isNull(object)</code><span><a class="mark" href="#utilisnullobject" id="utilisnullobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isnull_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>value === null</code> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is strictly <code>null</code>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isNull</span>(<span class="hljs-number">0</span>); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isNull</span>(<span class="hljs-literal">undefined</span>); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isNull</span>(<span class="hljs-literal">null</span>); <span class="hljs-comment">// Returns: true</span></code></pre> <h4><code>util.isNullOrUndefined(object)</code><span><a class="mark" href="#utilisnullorundefinedobject" id="utilisnullorundefinedobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isnullorundefined_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>value === undefined || value === null</code> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is <code>null</code> or <code>undefined</code>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isNullOrUndefined</span>(<span class="hljs-number">0</span>); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isNullOrUndefined</span>(<span class="hljs-literal">undefined</span>); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isNullOrUndefined</span>(<span class="hljs-literal">null</span>); <span class="hljs-comment">// Returns: true</span></code></pre> <h4><code>util.isNumber(object)</code><span><a class="mark" href="#utilisnumberobject" id="utilisnumberobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isnumber_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'number'</code> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is a <code>Number</code>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isNumber</span>(<span class="hljs-literal">false</span>); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isNumber</span>(<span class="hljs-title class_">Infinity</span>); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isNumber</span>(<span class="hljs-number">0</span>); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isNumber</span>(<span class="hljs-title class_">NaN</span>); <span class="hljs-comment">// Returns: true</span></code></pre> <h4><code>util.isObject(object)</code><span><a class="mark" href="#utilisobjectobject" id="utilisobjectobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isobject_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>value !== null && typeof value === 'object'</code> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is strictly an <code>Object</code> <strong>and</strong> not a <code>Function</code> (even though functions are objects in JavaScript). Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isObject</span>(<span class="hljs-number">5</span>); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isObject</span>(<span class="hljs-literal">null</span>); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isObject</span>({}); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isObject</span>(<span class="hljs-function">() =></span> {}); <span class="hljs-comment">// Returns: false</span></code></pre> <h4><code>util.isPrimitive(object)</code><span><a class="mark" href="#utilisprimitiveobject" id="utilisprimitiveobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isprimitive_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>(typeof value !== 'object' && typeof value !== 'function') || value === null</code> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is a primitive type. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-number">5</span>); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-string">'foo'</span>); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-literal">false</span>); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-literal">null</span>); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-literal">undefined</span>); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isPrimitive</span>({}); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-function">() =></span> {}); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-regexp">/^$/</span>); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>()); <span class="hljs-comment">// Returns: false</span></code></pre> <h4><code>util.isRegExp(object)</code><span><a class="mark" href="#utilisregexpobject" id="utilisregexpobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isregexp_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.6.0</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is a <code>RegExp</code>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isRegExp</span>(<span class="hljs-regexp">/some regexp/</span>); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isRegExp</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">RegExp</span>(<span class="hljs-string">'another regexp'</span>)); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isRegExp</span>({}); <span class="hljs-comment">// Returns: false</span></code></pre> <h4><code>util.isString(object)</code><span><a class="mark" href="#utilisstringobject" id="utilisstringobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isstring_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'string'</code> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is a <code>string</code>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isString</span>(<span class="hljs-string">''</span>); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isString</span>(<span class="hljs-string">'foo'</span>); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isString</span>(<span class="hljs-title class_">String</span>(<span class="hljs-string">'foo'</span>)); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isString</span>(<span class="hljs-number">5</span>); <span class="hljs-comment">// Returns: false</span></code></pre> <h4><code>util.isSymbol(object)</code><span><a class="mark" href="#utilissymbolobject" id="utilissymbolobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_issymbol_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'symbol'</code> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is a <code>Symbol</code>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">isSymbol</span>(<span class="hljs-number">5</span>); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isSymbol</span>(<span class="hljs-string">'foo'</span>); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isSymbol</span>(<span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'foo'</span>)); <span class="hljs-comment">// Returns: true</span></code></pre> <h4><code>util.isUndefined(object)</code><span><a class="mark" href="#utilisundefinedobject" id="utilisundefinedobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isundefined_object"></a></h4> <div class="api_metadata"> <span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>value === undefined</code> instead.</div><p></p> <ul> <li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Returns <code>true</code> if the given <code>object</code> is <code>undefined</code>. Otherwise, returns <code>false</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); <span class="hljs-keyword">const</span> foo = <span class="hljs-literal">undefined</span>; util.<span class="hljs-title function_">isUndefined</span>(<span class="hljs-number">5</span>); <span class="hljs-comment">// Returns: false</span> util.<span class="hljs-title function_">isUndefined</span>(foo); <span class="hljs-comment">// Returns: true</span> util.<span class="hljs-title function_">isUndefined</span>(<span class="hljs-literal">null</span>); <span class="hljs-comment">// Returns: false</span></code></pre> <h4><code>util.log(string)</code><span><a class="mark" href="#utillogstring" id="utillogstring">#</a></span><a aria-hidden="true" class="legacy" id="util_util_log_string"></a></h4> <div class="api_metadata"> <span>Added in: v0.3.0</span><span>Deprecated since: v6.0.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use a third party module instead.</div><p></p> <ul> <li><code>string</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>The <code>util.log()</code> method prints the given <code>string</code> to <code>stdout</code> with an included timestamp.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); util.<span class="hljs-title function_">log</span>(<span class="hljs-string">'Timestamped message.'</span>);</code></pre></section> <!-- API END --> </div> </div> </div> </body> </html>