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href="#performanceclearmarksname"><code>performance.clearMarks([name])</code></a></li> <li><a href="#performanceclearmeasuresname"><code>performance.clearMeasures([name])</code></a></li> <li><a href="#performanceclearresourcetimingsname"><code>performance.clearResourceTimings([name])</code></a></li> <li><a href="#performanceeventlooputilizationutilization1-utilization2"><code>performance.eventLoopUtilization([utilization1[, utilization2]])</code></a></li> <li><a href="#performancegetentries"><code>performance.getEntries()</code></a></li> <li><a href="#performancegetentriesbynamename-type"><code>performance.getEntriesByName(name[, type])</code></a></li> <li><a href="#performancegetentriesbytypetype"><code>performance.getEntriesByType(type)</code></a></li> <li><a href="#performancemarkname-options"><code>performance.mark([name[, options]])</code></a></li> <li><a href="#performancemarkresourcetimingtiminginfo-requestedurl-initiatortype-global-cachemode"><code>performance.markResourceTiming(timingInfo, requestedUrl, initiatorType, global, cacheMode)</code></a></li> <li><a href="#performancemeasurename-startmarkoroptions-endmark"><code>performance.measure(name[, startMarkOrOptions[, endMark]])</code></a></li> <li><a href="#performancenodetiming"><code>performance.nodeTiming</code></a></li> <li><a href="#performancenow"><code>performance.now()</code></a></li> <li><a href="#performancetimeorigin"><code>performance.timeOrigin</code></a></li> <li><a href="#performancetimerifyfn-options"><code>performance.timerify(fn[, options])</code></a></li> <li><a href="#performancetojson"><code>performance.toJSON()</code></a></li> </ul> </li> <li><a href="#class-performanceentry">Class: <code>PerformanceEntry</code></a> <ul> <li><a href="#performanceentrydetail"><code>performanceEntry.detail</code></a></li> <li><a href="#performanceentryduration"><code>performanceEntry.duration</code></a></li> <li><a href="#performanceentryentrytype"><code>performanceEntry.entryType</code></a></li> <li><a href="#performanceentryflags"><code>performanceEntry.flags</code></a></li> <li><a href="#performanceentryname"><code>performanceEntry.name</code></a></li> <li><a href="#performanceentrykind"><code>performanceEntry.kind</code></a></li> <li><a href="#performanceentrystarttime"><code>performanceEntry.startTime</code></a></li> <li><a href="#garbage-collection-gc-details">Garbage Collection ('gc') Details</a></li> <li><a href="#http-http-details">HTTP ('http') Details</a></li> <li><a href="#http2-http2-details">HTTP/2 ('http2') Details</a></li> <li><a href="#timerify-function-details">Timerify ('function') Details</a></li> <li><a href="#net-net-details">Net ('net') Details</a></li> <li><a href="#dns-dns-details">DNS ('dns') Details</a></li> </ul> </li> <li><a href="#class-performancenodetiming">Class: <code>PerformanceNodeTiming</code></a> <ul> <li><a href="#performancenodetimingbootstrapcomplete"><code>performanceNodeTiming.bootstrapComplete</code></a></li> <li><a href="#performancenodetimingenvironment"><code>performanceNodeTiming.environment</code></a></li> <li><a href="#performancenodetimingidletime"><code>performanceNodeTiming.idleTime</code></a></li> <li><a href="#performancenodetimingloopexit"><code>performanceNodeTiming.loopExit</code></a></li> <li><a href="#performancenodetimingloopstart"><code>performanceNodeTiming.loopStart</code></a></li> <li><a href="#performancenodetimingnodestart"><code>performanceNodeTiming.nodeStart</code></a></li> <li><a href="#performancenodetimingv8start"><code>performanceNodeTiming.v8Start</code></a></li> </ul> </li> <li><a href="#class-performanceresourcetiming">Class: <code>PerformanceResourceTiming</code></a> <ul> <li><a href="#performanceresourcetimingworkerstart"><code>performanceResourceTiming.workerStart</code></a></li> <li><a href="#performanceresourcetimingredirectstart"><code>performanceResourceTiming.redirectStart</code></a></li> <li><a href="#performanceresourcetimingredirectend"><code>performanceResourceTiming.redirectEnd</code></a></li> <li><a href="#performanceresourcetimingfetchstart"><code>performanceResourceTiming.fetchStart</code></a></li> <li><a href="#performanceresourcetimingdomainlookupstart"><code>performanceResourceTiming.domainLookupStart</code></a></li> <li><a href="#performanceresourcetimingdomainlookupend"><code>performanceResourceTiming.domainLookupEnd</code></a></li> <li><a href="#performanceresourcetimingconnectstart"><code>performanceResourceTiming.connectStart</code></a></li> <li><a href="#performanceresourcetimingconnectend"><code>performanceResourceTiming.connectEnd</code></a></li> <li><a href="#performanceresourcetimingsecureconnectionstart"><code>performanceResourceTiming.secureConnectionStart</code></a></li> <li><a href="#performanceresourcetimingrequeststart"><code>performanceResourceTiming.requestStart</code></a></li> <li><a href="#performanceresourcetimingresponseend"><code>performanceResourceTiming.responseEnd</code></a></li> <li><a href="#performanceresourcetimingtransfersize"><code>performanceResourceTiming.transferSize</code></a></li> <li><a href="#performanceresourcetimingencodedbodysize"><code>performanceResourceTiming.encodedBodySize</code></a></li> <li><a href="#performanceresourcetimingdecodedbodysize"><code>performanceResourceTiming.decodedBodySize</code></a></li> <li><a href="#performanceresourcetimingtojson"><code>performanceResourceTiming.toJSON()</code></a></li> </ul> </li> <li><a href="#class-perf_hooksperformanceobserver">Class: <code>perf_hooks.PerformanceObserver</code></a> <ul> <li><a href="#new-performanceobservercallback"><code>new PerformanceObserver(callback)</code></a></li> <li><a href="#performanceobserverdisconnect"><code>performanceObserver.disconnect()</code></a></li> <li><a href="#performanceobserverobserveoptions"><code>performanceObserver.observe(options)</code></a></li> </ul> </li> <li><a href="#class-performanceobserverentrylist">Class: <code>PerformanceObserverEntryList</code></a> <ul> <li><a href="#performanceobserverentrylistgetentries"><code>performanceObserverEntryList.getEntries()</code></a></li> <li><a href="#performanceobserverentrylistgetentriesbynamename-type"><code>performanceObserverEntryList.getEntriesByName(name[, type])</code></a></li> <li><a href="#performanceobserverentrylistgetentriesbytypetype"><code>performanceObserverEntryList.getEntriesByType(type)</code></a></li> </ul> </li> <li><a href="#perf_hookscreatehistogramoptions"><code>perf_hooks.createHistogram([options])</code></a></li> <li><a href="#perf_hooksmonitoreventloopdelayoptions"><code>perf_hooks.monitorEventLoopDelay([options])</code></a></li> <li><a href="#class-histogram">Class: <code>Histogram</code></a> <ul> <li><a href="#histogramcount"><code>histogram.count</code></a></li> <li><a href="#histogramcountbigint"><code>histogram.countBigInt</code></a></li> <li><a href="#histogramexceeds"><code>histogram.exceeds</code></a></li> <li><a href="#histogramexceedsbigint"><code>histogram.exceedsBigInt</code></a></li> <li><a href="#histogrammax"><code>histogram.max</code></a></li> <li><a href="#histogrammaxbigint"><code>histogram.maxBigInt</code></a></li> <li><a href="#histogrammean"><code>histogram.mean</code></a></li> <li><a href="#histogrammin"><code>histogram.min</code></a></li> <li><a href="#histogramminbigint"><code>histogram.minBigInt</code></a></li> <li><a href="#histogrampercentilepercentile"><code>histogram.percentile(percentile)</code></a></li> <li><a href="#histogrampercentilebigintpercentile"><code>histogram.percentileBigInt(percentile)</code></a></li> <li><a href="#histogrampercentiles"><code>histogram.percentiles</code></a></li> <li><a href="#histogrampercentilesbigint"><code>histogram.percentilesBigInt</code></a></li> <li><a href="#histogramreset"><code>histogram.reset()</code></a></li> <li><a href="#histogramstddev"><code>histogram.stddev</code></a></li> </ul> </li> <li><a href="#class-intervalhistogram-extends-histogram">Class: <code>IntervalHistogram extends Histogram</code></a> <ul> <li><a href="#histogramdisable"><code>histogram.disable()</code></a></li> <li><a href="#histogramenable"><code>histogram.enable()</code></a></li> <li><a href="#cloning-an-intervalhistogram">Cloning an <code>IntervalHistogram</code></a></li> </ul> </li> <li><a href="#class-recordablehistogram-extends-histogram">Class: <code>RecordableHistogram extends Histogram</code></a> <ul> <li><a href="#histogramaddother"><code>histogram.add(other)</code></a></li> <li><a href="#histogramrecordval"><code>histogram.record(val)</code></a></li> <li><a href="#histogramrecorddelta"><code>histogram.recordDelta()</code></a></li> </ul> </li> <li><a href="#examples">Examples</a> <ul> <li><a href="#measuring-the-duration-of-async-operations">Measuring the duration of async operations</a></li> <li><a href="#measuring-how-long-it-takes-to-load-dependencies">Measuring how long it takes to load dependencies</a></li> <li><a href="#measuring-how-long-one-http-round-trip-takes">Measuring how long one HTTP round-trip takes</a></li> <li><a href="#measuring-how-long-the-netconnect-only-for-tcp-takes-when-the-connection-is-successful">Measuring how long the <code>net.connect</code> (only for TCP) takes when the connection is successful</a></li> <li><a href="#measuring-how-long-the-dns-takes-when-the-request-is-successful">Measuring how long the DNS takes when the request is successful</a></li> </ul> </li> </ul> </li> </ul></div></div> </li> <li class="picker-header"> <a href="#"> <span class="collapsed-arrow">►</span><span 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href="https://nodejs.org/docs/latest-v16.x/api/perf_hooks.html">16.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v15.x/api/perf_hooks.html">15.x</a></li> <li><a href="https://nodejs.org/docs/latest-v14.x/api/perf_hooks.html">14.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v13.x/api/perf_hooks.html">13.x</a></li> <li><a href="https://nodejs.org/docs/latest-v12.x/api/perf_hooks.html">12.x</a></li> <li><a href="https://nodejs.org/docs/latest-v11.x/api/perf_hooks.html">11.x</a></li> <li><a href="https://nodejs.org/docs/latest-v10.x/api/perf_hooks.html">10.x</a></li> <li><a href="https://nodejs.org/docs/latest-v9.x/api/perf_hooks.html">9.x</a></li> <li><a href="https://nodejs.org/docs/latest-v8.x/api/perf_hooks.html">8.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="perf_hooks.json">View as JSON</a> </li> <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/perf_hooks.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="#performance-measurement-apis">Performance measurement APIs</a></span> <ul> <li><a href="#perf_hooksperformance"><code>perf_hooks.performance</code></a> <ul> <li><a href="#performanceclearmarksname"><code>performance.clearMarks([name])</code></a></li> <li><a href="#performanceclearmeasuresname"><code>performance.clearMeasures([name])</code></a></li> <li><a href="#performanceclearresourcetimingsname"><code>performance.clearResourceTimings([name])</code></a></li> <li><a href="#performanceeventlooputilizationutilization1-utilization2"><code>performance.eventLoopUtilization([utilization1[, utilization2]])</code></a></li> <li><a href="#performancegetentries"><code>performance.getEntries()</code></a></li> <li><a href="#performancegetentriesbynamename-type"><code>performance.getEntriesByName(name[, type])</code></a></li> <li><a href="#performancegetentriesbytypetype"><code>performance.getEntriesByType(type)</code></a></li> <li><a href="#performancemarkname-options"><code>performance.mark([name[, options]])</code></a></li> <li><a href="#performancemarkresourcetimingtiminginfo-requestedurl-initiatortype-global-cachemode"><code>performance.markResourceTiming(timingInfo, requestedUrl, initiatorType, global, cacheMode)</code></a></li> <li><a href="#performancemeasurename-startmarkoroptions-endmark"><code>performance.measure(name[, startMarkOrOptions[, endMark]])</code></a></li> <li><a href="#performancenodetiming"><code>performance.nodeTiming</code></a></li> <li><a href="#performancenow"><code>performance.now()</code></a></li> <li><a href="#performancetimeorigin"><code>performance.timeOrigin</code></a></li> <li><a href="#performancetimerifyfn-options"><code>performance.timerify(fn[, options])</code></a></li> <li><a href="#performancetojson"><code>performance.toJSON()</code></a></li> </ul> </li> <li><a href="#class-performanceentry">Class: <code>PerformanceEntry</code></a> <ul> <li><a href="#performanceentrydetail"><code>performanceEntry.detail</code></a></li> <li><a href="#performanceentryduration"><code>performanceEntry.duration</code></a></li> <li><a href="#performanceentryentrytype"><code>performanceEntry.entryType</code></a></li> <li><a href="#performanceentryflags"><code>performanceEntry.flags</code></a></li> <li><a href="#performanceentryname"><code>performanceEntry.name</code></a></li> <li><a href="#performanceentrykind"><code>performanceEntry.kind</code></a></li> <li><a href="#performanceentrystarttime"><code>performanceEntry.startTime</code></a></li> <li><a href="#garbage-collection-gc-details">Garbage Collection ('gc') Details</a></li> <li><a href="#http-http-details">HTTP ('http') Details</a></li> <li><a href="#http2-http2-details">HTTP/2 ('http2') Details</a></li> <li><a href="#timerify-function-details">Timerify ('function') Details</a></li> <li><a href="#net-net-details">Net ('net') Details</a></li> <li><a href="#dns-dns-details">DNS ('dns') Details</a></li> </ul> </li> <li><a href="#class-performancenodetiming">Class: <code>PerformanceNodeTiming</code></a> <ul> <li><a href="#performancenodetimingbootstrapcomplete"><code>performanceNodeTiming.bootstrapComplete</code></a></li> <li><a href="#performancenodetimingenvironment"><code>performanceNodeTiming.environment</code></a></li> <li><a href="#performancenodetimingidletime"><code>performanceNodeTiming.idleTime</code></a></li> <li><a href="#performancenodetimingloopexit"><code>performanceNodeTiming.loopExit</code></a></li> <li><a href="#performancenodetimingloopstart"><code>performanceNodeTiming.loopStart</code></a></li> <li><a href="#performancenodetimingnodestart"><code>performanceNodeTiming.nodeStart</code></a></li> <li><a href="#performancenodetimingv8start"><code>performanceNodeTiming.v8Start</code></a></li> </ul> </li> <li><a href="#class-performanceresourcetiming">Class: <code>PerformanceResourceTiming</code></a> <ul> <li><a href="#performanceresourcetimingworkerstart"><code>performanceResourceTiming.workerStart</code></a></li> <li><a href="#performanceresourcetimingredirectstart"><code>performanceResourceTiming.redirectStart</code></a></li> <li><a href="#performanceresourcetimingredirectend"><code>performanceResourceTiming.redirectEnd</code></a></li> <li><a href="#performanceresourcetimingfetchstart"><code>performanceResourceTiming.fetchStart</code></a></li> <li><a href="#performanceresourcetimingdomainlookupstart"><code>performanceResourceTiming.domainLookupStart</code></a></li> <li><a href="#performanceresourcetimingdomainlookupend"><code>performanceResourceTiming.domainLookupEnd</code></a></li> <li><a href="#performanceresourcetimingconnectstart"><code>performanceResourceTiming.connectStart</code></a></li> <li><a href="#performanceresourcetimingconnectend"><code>performanceResourceTiming.connectEnd</code></a></li> <li><a href="#performanceresourcetimingsecureconnectionstart"><code>performanceResourceTiming.secureConnectionStart</code></a></li> <li><a href="#performanceresourcetimingrequeststart"><code>performanceResourceTiming.requestStart</code></a></li> <li><a href="#performanceresourcetimingresponseend"><code>performanceResourceTiming.responseEnd</code></a></li> <li><a href="#performanceresourcetimingtransfersize"><code>performanceResourceTiming.transferSize</code></a></li> <li><a href="#performanceresourcetimingencodedbodysize"><code>performanceResourceTiming.encodedBodySize</code></a></li> <li><a href="#performanceresourcetimingdecodedbodysize"><code>performanceResourceTiming.decodedBodySize</code></a></li> <li><a href="#performanceresourcetimingtojson"><code>performanceResourceTiming.toJSON()</code></a></li> </ul> </li> <li><a href="#class-perf_hooksperformanceobserver">Class: <code>perf_hooks.PerformanceObserver</code></a> <ul> <li><a href="#new-performanceobservercallback"><code>new PerformanceObserver(callback)</code></a></li> <li><a href="#performanceobserverdisconnect"><code>performanceObserver.disconnect()</code></a></li> <li><a href="#performanceobserverobserveoptions"><code>performanceObserver.observe(options)</code></a></li> </ul> </li> <li><a href="#class-performanceobserverentrylist">Class: <code>PerformanceObserverEntryList</code></a> <ul> <li><a href="#performanceobserverentrylistgetentries"><code>performanceObserverEntryList.getEntries()</code></a></li> <li><a href="#performanceobserverentrylistgetentriesbynamename-type"><code>performanceObserverEntryList.getEntriesByName(name[, type])</code></a></li> <li><a href="#performanceobserverentrylistgetentriesbytypetype"><code>performanceObserverEntryList.getEntriesByType(type)</code></a></li> </ul> </li> <li><a href="#perf_hookscreatehistogramoptions"><code>perf_hooks.createHistogram([options])</code></a></li> <li><a href="#perf_hooksmonitoreventloopdelayoptions"><code>perf_hooks.monitorEventLoopDelay([options])</code></a></li> <li><a href="#class-histogram">Class: <code>Histogram</code></a> <ul> <li><a href="#histogramcount"><code>histogram.count</code></a></li> <li><a href="#histogramcountbigint"><code>histogram.countBigInt</code></a></li> <li><a href="#histogramexceeds"><code>histogram.exceeds</code></a></li> <li><a href="#histogramexceedsbigint"><code>histogram.exceedsBigInt</code></a></li> <li><a href="#histogrammax"><code>histogram.max</code></a></li> <li><a href="#histogrammaxbigint"><code>histogram.maxBigInt</code></a></li> <li><a href="#histogrammean"><code>histogram.mean</code></a></li> <li><a href="#histogrammin"><code>histogram.min</code></a></li> <li><a href="#histogramminbigint"><code>histogram.minBigInt</code></a></li> <li><a href="#histogrampercentilepercentile"><code>histogram.percentile(percentile)</code></a></li> <li><a href="#histogrampercentilebigintpercentile"><code>histogram.percentileBigInt(percentile)</code></a></li> <li><a href="#histogrampercentiles"><code>histogram.percentiles</code></a></li> <li><a href="#histogrampercentilesbigint"><code>histogram.percentilesBigInt</code></a></li> <li><a href="#histogramreset"><code>histogram.reset()</code></a></li> <li><a href="#histogramstddev"><code>histogram.stddev</code></a></li> </ul> </li> <li><a href="#class-intervalhistogram-extends-histogram">Class: <code>IntervalHistogram extends Histogram</code></a> <ul> <li><a href="#histogramdisable"><code>histogram.disable()</code></a></li> <li><a href="#histogramenable"><code>histogram.enable()</code></a></li> <li><a href="#cloning-an-intervalhistogram">Cloning an <code>IntervalHistogram</code></a></li> </ul> </li> <li><a href="#class-recordablehistogram-extends-histogram">Class: <code>RecordableHistogram extends Histogram</code></a> <ul> <li><a href="#histogramaddother"><code>histogram.add(other)</code></a></li> <li><a href="#histogramrecordval"><code>histogram.record(val)</code></a></li> <li><a href="#histogramrecorddelta"><code>histogram.recordDelta()</code></a></li> </ul> </li> <li><a href="#examples">Examples</a> <ul> <li><a href="#measuring-the-duration-of-async-operations">Measuring the duration of async operations</a></li> <li><a href="#measuring-how-long-it-takes-to-load-dependencies">Measuring how long it takes to load dependencies</a></li> <li><a href="#measuring-how-long-one-http-round-trip-takes">Measuring how long one HTTP round-trip takes</a></li> <li><a href="#measuring-how-long-the-netconnect-only-for-tcp-takes-when-the-connection-is-successful">Measuring how long the <code>net.connect</code> (only for TCP) takes when the connection is successful</a></li> <li><a href="#measuring-how-long-the-dns-takes-when-the-request-is-successful">Measuring how long the DNS takes when the request is successful</a></li> </ul> </li> </ul> </li> </ul></details> <div id="apicontent"> <h2>Performance measurement APIs<span><a class="mark" href="#performance-measurement-apis" id="performance-measurement-apis">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_measurement_apis"></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/perf_hooks.js">lib/perf_hooks.js</a></p> <p>This module provides an implementation of a subset of the W3C <a href="https://w3c.github.io/perf-timing-primer/">Web Performance APIs</a> as well as additional APIs for Node.js-specific performance measurements.</p> <p>Node.js supports the following <a href="https://w3c.github.io/perf-timing-primer/">Web Performance APIs</a>:</p> <ul> <li><a href="https://www.w3.org/TR/hr-time-2">High Resolution Time</a></li> <li><a href="https://w3c.github.io/performance-timeline/">Performance Timeline</a></li> <li><a href="https://www.w3.org/TR/user-timing/">User Timing</a></li> <li><a href="https://www.w3.org/TR/resource-timing-2/">Resource Timing</a></li> </ul> <pre><code class="language-js"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">PerformanceObserver</span>, performance } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">items</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(items.<span class="hljs-title function_">getEntries</span>()[<span class="hljs-number">0</span>].<span class="hljs-property">duration</span>); performance.<span class="hljs-title function_">clearMarks</span>(); }); obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">type</span>: <span class="hljs-string">'measure'</span> }); performance.<span class="hljs-title function_">measure</span>(<span class="hljs-string">'Start to Now'</span>); performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'A'</span>); <span class="hljs-title function_">doSomeLongRunningProcess</span>(<span class="hljs-function">() =></span> { performance.<span class="hljs-title function_">measure</span>(<span class="hljs-string">'A to Now'</span>, <span class="hljs-string">'A'</span>); performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'B'</span>); performance.<span class="hljs-title function_">measure</span>(<span class="hljs-string">'A to B'</span>, <span class="hljs-string">'A'</span>, <span class="hljs-string">'B'</span>); });</code></pre> <section><h3><code>perf_hooks.performance</code><span><a class="mark" href="#perf_hooksperformance" id="perf_hooksperformance">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_perf_hooks_performance"></a></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <p>An object that can be used to collect performance metrics from the current Node.js instance. It is similar to <a href="https://developer.mozilla.org/en-US/docs/Web/API/Window/performance"><code>window.performance</code></a> in browsers.</p> <h4><code>performance.clearMarks([name])</code><span><a class="mark" href="#performanceclearmarksname" id="performanceclearmarksname">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_clearmarks_name"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>If <code>name</code> is not provided, removes all <code>PerformanceMark</code> objects from the Performance Timeline. If <code>name</code> is provided, removes only the named mark.</p> <h4><code>performance.clearMeasures([name])</code><span><a class="mark" href="#performanceclearmeasuresname" id="performanceclearmeasuresname">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_clearmeasures_name"></a></h4> <div class="api_metadata"> <span>Added in: v16.7.0</span> </div> <ul> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>If <code>name</code> is not provided, removes all <code>PerformanceMeasure</code> objects from the Performance Timeline. If <code>name</code> is provided, removes only the named measure.</p> <h4><code>performance.clearResourceTimings([name])</code><span><a class="mark" href="#performanceclearresourcetimingsname" id="performanceclearresourcetimingsname">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_clearresourcetimings_name"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>If <code>name</code> is not provided, removes all <code>PerformanceResourceTiming</code> objects from the Resource Timeline. If <code>name</code> is provided, removes only the named resource.</p> <h4><code>performance.eventLoopUtilization([utilization1[, utilization2]])</code><span><a class="mark" href="#performanceeventlooputilizationutilization1-utilization2" id="performanceeventlooputilizationutilization1-utilization2">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_eventlooputilization_utilization1_utilization2"></a></h4> <div class="api_metadata"> <span>Added in: v14.10.0, v12.19.0</span> </div> <ul> <li><code>utilization1</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The result of a previous call to <code>eventLoopUtilization()</code>.</li> <li><code>utilization2</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The result of a previous call to <code>eventLoopUtilization()</code> prior to <code>utilization1</code>.</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>idle</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>active</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>utilization</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> </li> </ul> <p>The <code>eventLoopUtilization()</code> method returns an object that contains the cumulative duration of time the event loop has been both idle and active as a high resolution milliseconds timer. The <code>utilization</code> value is the calculated Event Loop Utilization (ELU).</p> <p>If bootstrapping has not yet finished on the main thread the properties have the value of <code>0</code>. The ELU is immediately available on <a href="worker_threads.html#worker-threads">Worker threads</a> since bootstrap happens within the event loop.</p> <p>Both <code>utilization1</code> and <code>utilization2</code> are optional parameters.</p> <p>If <code>utilization1</code> is passed, then the delta between the current call's <code>active</code> and <code>idle</code> times, as well as the corresponding <code>utilization</code> value are calculated and returned (similar to <a href="process.html#processhrtimetime"><code>process.hrtime()</code></a>).</p> <p>If <code>utilization1</code> and <code>utilization2</code> are both passed, then the delta is calculated between the two arguments. This is a convenience option because, unlike <a href="process.html#processhrtimetime"><code>process.hrtime()</code></a>, calculating the ELU is more complex than a single subtraction.</p> <p>ELU is similar to CPU utilization, except that it only measures event loop statistics and not CPU usage. It represents the percentage of time the event loop has spent outside the event loop's event provider (e.g. <code>epoll_wait</code>). No other CPU idle time is taken into consideration. The following is an example of how a mostly idle process will have a high ELU.</p> <pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; <span class="hljs-keyword">const</span> { eventLoopUtilization } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>).<span class="hljs-property">performance</span>; <span class="hljs-keyword">const</span> { spawnSync } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:child_process'</span>); <span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> { <span class="hljs-keyword">const</span> elu = <span class="hljs-title function_">eventLoopUtilization</span>(); <span class="hljs-title function_">spawnSync</span>(<span class="hljs-string">'sleep'</span>, [<span class="hljs-string">'5'</span>]); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">eventLoopUtilization</span>(elu).<span class="hljs-property">utilization</span>); });</code></pre> <p>Although the CPU is mostly idle while running this script, the value of <code>utilization</code> is <code>1</code>. This is because the call to <a href="child_process.html#child_processspawnsynccommand-args-options"><code>child_process.spawnSync()</code></a> blocks the event loop from proceeding.</p> <p>Passing in a user-defined object instead of the result of a previous call to <code>eventLoopUtilization()</code> will lead to undefined behavior. The return values are not guaranteed to reflect any correct state of the event loop.</p> <h4><code>performance.getEntries()</code><span><a class="mark" href="#performancegetentries" id="performancegetentries">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_getentries"></a></h4> <div class="api_metadata"> <span>Added in: v16.7.0</span> </div> <ul> <li>Returns: <a href="perf_hooks.html#class-performanceentry" class="type"><PerformanceEntry[]></a></li> </ul> <p>Returns a list of <code>PerformanceEntry</code> objects in chronological order with respect to <code>performanceEntry.startTime</code>. If you are only interested in performance entries of certain types or that have certain names, see <code>performance.getEntriesByType()</code> and <code>performance.getEntriesByName()</code>.</p> <h4><code>performance.getEntriesByName(name[, type])</code><span><a class="mark" href="#performancegetentriesbynamename-type" id="performancegetentriesbynamename-type">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_getentriesbyname_name_type"></a></h4> <div class="api_metadata"> <span>Added in: v16.7.0</span> </div> <ul> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> <li><code>type</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="perf_hooks.html#class-performanceentry" class="type"><PerformanceEntry[]></a></li> </ul> <p>Returns a list of <code>PerformanceEntry</code> objects in chronological order with respect to <code>performanceEntry.startTime</code> whose <code>performanceEntry.name</code> is equal to <code>name</code>, and optionally, whose <code>performanceEntry.entryType</code> is equal to <code>type</code>.</p> <h4><code>performance.getEntriesByType(type)</code><span><a class="mark" href="#performancegetentriesbytypetype" id="performancegetentriesbytypetype">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_getentriesbytype_type"></a></h4> <div class="api_metadata"> <span>Added in: v16.7.0</span> </div> <ul> <li><code>type</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="perf_hooks.html#class-performanceentry" class="type"><PerformanceEntry[]></a></li> </ul> <p>Returns a list of <code>PerformanceEntry</code> objects in chronological order with respect to <code>performanceEntry.startTime</code> whose <code>performanceEntry.entryType</code> is equal to <code>type</code>.</p> <h4><code>performance.mark([name[, options]])</code><span><a class="mark" href="#performancemarkname-options" id="performancemarkname-options">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_mark_name_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>v16.0.0</td> <td><p>Updated to conform to the User Timing Level 3 specification.</p></td></tr> <tr><td>v8.5.0</td> <td><p><span>Added in: v8.5.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></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>detail</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Additional optional detail to include with the mark.</li> <li><code>startTime</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> An optional timestamp to be used as the mark time. <strong>Default</strong>: <code>performance.now()</code>.</li> </ul> </li> </ul> <p>Creates a new <code>PerformanceMark</code> entry in the Performance Timeline. A <code>PerformanceMark</code> is a subclass of <code>PerformanceEntry</code> whose <code>performanceEntry.entryType</code> is always <code>'mark'</code>, and whose <code>performanceEntry.duration</code> is always <code>0</code>. Performance marks are used to mark specific significant moments in the Performance Timeline.</p> <p>The created <code>PerformanceMark</code> entry is put in the global Performance Timeline and can be queried with <code>performance.getEntries</code>, <code>performance.getEntriesByName</code>, and <code>performance.getEntriesByType</code>. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with <code>performance.clearMarks</code>.</p> <h4><code>performance.markResourceTiming(timingInfo, requestedUrl, initiatorType, global, cacheMode)</code><span><a class="mark" href="#performancemarkresourcetimingtiminginfo-requestedurl-initiatortype-global-cachemode" id="performancemarkresourcetimingtiminginfo-requestedurl-initiatortype-global-cachemode">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_markresourcetiming_timinginfo_requestedurl_initiatortype_global_cachemode"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><code>timingInfo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> <a href="https://fetch.spec.whatwg.org/#fetch-timing-info">Fetch Timing Info</a></li> <li><code>requestedUrl</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The resource url</li> <li><code>initiatorType</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The initiator name, e.g: 'fetch'</li> <li><code>global</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> <li><code>cacheMode</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The cache mode must be an empty string ('') or 'local'</li> </ul> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>Creates a new <code>PerformanceResourceTiming</code> entry in the Resource Timeline. A <code>PerformanceResourceTiming</code> is a subclass of <code>PerformanceEntry</code> whose <code>performanceEntry.entryType</code> is always <code>'resource'</code>. Performance resources are used to mark moments in the Resource Timeline.</p> <p>The created <code>PerformanceMark</code> entry is put in the global Resource Timeline and can be queried with <code>performance.getEntries</code>, <code>performance.getEntriesByName</code>, and <code>performance.getEntriesByType</code>. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with <code>performance.clearResourceTimings</code>.</p> <h4><code>performance.measure(name[, startMarkOrOptions[, endMark]])</code><span><a class="mark" href="#performancemeasurename-startmarkoroptions-endmark" id="performancemeasurename-startmarkoroptions-endmark">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_measure_name_startmarkoroptions_endmark"></a></h4> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v16.0.0</td> <td><p>Updated to conform to the User Timing Level 3 specification.</p></td></tr> <tr><td>v13.13.0, v12.16.3</td> <td><p>Make <code>startMark</code> and <code>endMark</code> parameters optional.</p></td></tr> <tr><td>v8.5.0</td> <td><p><span>Added in: v8.5.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> <li><code>startMarkOrOptions</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/Reference/Global_Objects/Object" class="type"><Object></a> Optional. <ul> <li><code>detail</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Additional optional detail to include with the measure.</li> <li><code>duration</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Duration between start and end times.</li> <li><code>end</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Timestamp to be used as the end time, or a string identifying a previously recorded mark.</li> <li><code>start</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Timestamp to be used as the start time, or a string identifying a previously recorded mark.</li> </ul> </li> <li><code>endMark</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Optional. Must be omitted if <code>startMarkOrOptions</code> is an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>.</li> </ul> <p>Creates a new <code>PerformanceMeasure</code> entry in the Performance Timeline. A <code>PerformanceMeasure</code> is a subclass of <code>PerformanceEntry</code> whose <code>performanceEntry.entryType</code> is always <code>'measure'</code>, and whose <code>performanceEntry.duration</code> measures the number of milliseconds elapsed since <code>startMark</code> and <code>endMark</code>.</p> <p>The <code>startMark</code> argument may identify any <em>existing</em> <code>PerformanceMark</code> in the Performance Timeline, or <em>may</em> identify any of the timestamp properties provided by the <code>PerformanceNodeTiming</code> class. If the named <code>startMark</code> does not exist, an error is thrown.</p> <p>The optional <code>endMark</code> argument must identify any <em>existing</em> <code>PerformanceMark</code> in the Performance Timeline or any of the timestamp properties provided by the <code>PerformanceNodeTiming</code> class. <code>endMark</code> will be <code>performance.now()</code> if no parameter is passed, otherwise if the named <code>endMark</code> does not exist, an error will be thrown.</p> <p>The created <code>PerformanceMeasure</code> entry is put in the global Performance Timeline and can be queried with <code>performance.getEntries</code>, <code>performance.getEntriesByName</code>, and <code>performance.getEntriesByType</code>. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with <code>performance.clearMeasures</code>.</p> <h4><code>performance.nodeTiming</code><span><a class="mark" href="#performancenodetiming" id="performancenodetiming">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_nodetiming"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="perf_hooks.html#class-performancenodetiming" class="type"><PerformanceNodeTiming></a></li> </ul> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>An instance of the <code>PerformanceNodeTiming</code> class that provides performance metrics for specific Node.js operational milestones.</p> <h4><code>performance.now()</code><span><a class="mark" href="#performancenow" id="performancenow">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_now"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>Returns the current high resolution millisecond timestamp, where 0 represents the start of the current <code>node</code> process.</p> <h4><code>performance.timeOrigin</code><span><a class="mark" href="#performancetimeorigin" id="performancetimeorigin">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_timeorigin"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The <a href="https://w3c.github.io/hr-time/#dom-performance-timeorigin"><code>timeOrigin</code></a> specifies the high resolution millisecond timestamp at which the current <code>node</code> process began, measured in Unix time.</p> <h4><code>performance.timerify(fn[, options])</code><span><a class="mark" href="#performancetimerifyfn-options" id="performancetimerifyfn-options">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_timerify_fn_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>v16.0.0</td> <td><p>Added the histogram option.</p></td></tr> <tr><td>v16.0.0</td> <td><p>Re-implemented to use pure-JavaScript and the ability to time async functions.</p></td></tr> <tr><td>v8.5.0</td> <td><p><span>Added in: v8.5.0</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></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>histogram</code> <a href="perf_hooks.html#class-recordablehistogram-extends-histogram" class="type"><RecordableHistogram></a> A histogram object created using <code>perf_hooks.createHistogram()</code> that will record runtime durations in nanoseconds.</li> </ul> </li> </ul> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>Wraps a function within a new function that measures the running time of the wrapped function. A <code>PerformanceObserver</code> must be subscribed to the <code>'function'</code> event type in order for the timing details to be accessed.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { performance, <span class="hljs-title class_">PerformanceObserver</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">function</span> <span class="hljs-title function_">someFunction</span>(<span class="hljs-params"></span>) { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'hello world'</span>); } <span class="hljs-keyword">const</span> wrapped = performance.<span class="hljs-title function_">timerify</span>(someFunction); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">list</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(list.<span class="hljs-title function_">getEntries</span>()[<span class="hljs-number">0</span>].<span class="hljs-property">duration</span>); performance.<span class="hljs-title function_">clearMarks</span>(); performance.<span class="hljs-title function_">clearMeasures</span>(); obs.<span class="hljs-title function_">disconnect</span>(); }); obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'function'</span>] }); <span class="hljs-comment">// A performance timeline entry will be created</span> <span class="hljs-title function_">wrapped</span>();</code></pre> <p>If the wrapped function returns a promise, a finally handler will be attached to the promise and the duration will be reported once the finally handler is invoked.</p> <h4><code>performance.toJSON()</code><span><a class="mark" href="#performancetojson" id="performancetojson">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performance_tojson"></a></h4> <div class="api_metadata"> <span>Added in: v16.1.0</span> </div> <p>An object which is JSON representation of the <code>performance</code> object. It is similar to <a href="https://developer.mozilla.org/en-US/docs/Web/API/Performance/toJSON"><code>window.performance.toJSON</code></a> in browsers.</p> </section><section><h3>Class: <code>PerformanceEntry</code><span><a class="mark" href="#class-performanceentry" id="class-performanceentry">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_class_performanceentry"></a></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <h4><code>performanceEntry.detail</code><span><a class="mark" href="#performanceentrydetail" id="performanceentrydetail">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceentry_detail"></a></h4> <div class="api_metadata"> <span>Added in: v16.0.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> </ul> <p>Additional detail specific to the <code>entryType</code>.</p> <h4><code>performanceEntry.duration</code><span><a class="mark" href="#performanceentryduration" id="performanceentryduration">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceentry_duration"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The total number of milliseconds elapsed for this entry. This value will not be meaningful for all Performance Entry types.</p> <h4><code>performanceEntry.entryType</code><span><a class="mark" href="#performanceentryentrytype" id="performanceentryentrytype">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceentry_entrytype"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <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 type of the performance entry. It may be one of:</p> <ul> <li><code>'node'</code> (Node.js only)</li> <li><code>'mark'</code> (available on the Web)</li> <li><code>'measure'</code> (available on the Web)</li> <li><code>'gc'</code> (Node.js only)</li> <li><code>'function'</code> (Node.js only)</li> <li><code>'http2'</code> (Node.js only)</li> <li><code>'http'</code> (Node.js only)</li> </ul> <h4><code>performanceEntry.flags</code><span><a class="mark" href="#performanceentryflags" id="performanceentryflags">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceentry_flags"></a></h4> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v16.0.0</td> <td><p>Runtime deprecated. Now moved to the detail property when entryType is 'gc'.</p></td></tr> <tr><td>v13.9.0, v12.17.0</td> <td><p><span>Added in: v13.9.0, v12.17.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>When <code>performanceEntry.entryType</code> is equal to <code>'gc'</code>, the <code>performance.flags</code> property contains additional information about garbage collection operation. The value may be one of:</p> <ul> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE</code></li> </ul> <h4><code>performanceEntry.name</code><span><a class="mark" href="#performanceentryname" id="performanceentryname">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceentry_name"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <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 name of the performance entry.</p> <h4><code>performanceEntry.kind</code><span><a class="mark" href="#performanceentrykind" id="performanceentrykind">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceentry_kind"></a></h4> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v16.0.0</td> <td><p>Runtime deprecated. Now moved to the detail property when entryType is 'gc'.</p></td></tr> <tr><td>v8.5.0</td> <td><p><span>Added in: v8.5.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>When <code>performanceEntry.entryType</code> is equal to <code>'gc'</code>, the <code>performance.kind</code> property identifies the type of garbage collection operation that occurred. The value may be one of:</p> <ul> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB</code></li> </ul> <h4><code>performanceEntry.startTime</code><span><a class="mark" href="#performanceentrystarttime" id="performanceentrystarttime">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceentry_starttime"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp marking the starting time of the Performance Entry.</p> <h4>Garbage Collection ('gc') Details<span><a class="mark" href="#garbage-collection-gc-details" id="garbage-collection-gc-details">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_garbage_collection_gc_details"></a></h4> <p>When <code>performanceEntry.type</code> is equal to <code>'gc'</code>, the <code>performanceEntry.detail</code> property will be an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> with two properties:</p> <ul> <li><code>kind</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> One of: <ul> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB</code></li> </ul> </li> <li><code>flags</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> One of: <ul> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE</code></li> </ul> </li> </ul> <h4>HTTP ('http') Details<span><a class="mark" href="#http-http-details" id="http-http-details">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_http_http_details"></a></h4> <p>When <code>performanceEntry.type</code> is equal to <code>'http'</code>, the <code>performanceEntry.detail</code> property will be an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> containing additional information.</p> <p>If <code>performanceEntry.name</code> is equal to <code>HttpClient</code>, the <code>detail</code> will contain the following properties: <code>req</code>, <code>res</code>. And the <code>req</code> property will be an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> containing <code>method</code>, <code>url</code>, <code>headers</code>, the <code>res</code> property will be an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> containing <code>statusCode</code>, <code>statusMessage</code>, <code>headers</code>.</p> <p>If <code>performanceEntry.name</code> is equal to <code>HttpRequest</code>, the <code>detail</code> will contain the following properties: <code>req</code>, <code>res</code>. And the <code>req</code> property will be an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> containing <code>method</code>, <code>url</code>, <code>headers</code>, the <code>res</code> property will be an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> containing <code>statusCode</code>, <code>statusMessage</code>, <code>headers</code>.</p> <p>This could add additional memory overhead and should only be used for diagnostic purposes, not left turned on in production by default.</p> <h4>HTTP/2 ('http2') Details<span><a class="mark" href="#http2-http2-details" id="http2-http2-details">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_http_2_http2_details"></a></h4> <p>When <code>performanceEntry.type</code> is equal to <code>'http2'</code>, the <code>performanceEntry.detail</code> property will be an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> containing additional performance information.</p> <p>If <code>performanceEntry.name</code> is equal to <code>Http2Stream</code>, the <code>detail</code> will contain the following properties:</p> <ul> <li><code>bytesRead</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of <code>DATA</code> frame bytes received for this <code>Http2Stream</code>.</li> <li><code>bytesWritten</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of <code>DATA</code> frame bytes sent for this <code>Http2Stream</code>.</li> <li><code>id</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The identifier of the associated <code>Http2Stream</code></li> <li><code>timeToFirstByte</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of milliseconds elapsed between the <code>PerformanceEntry</code> <code>startTime</code> and the reception of the first <code>DATA</code> frame.</li> <li><code>timeToFirstByteSent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of milliseconds elapsed between the <code>PerformanceEntry</code> <code>startTime</code> and sending of the first <code>DATA</code> frame.</li> <li><code>timeToFirstHeader</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of milliseconds elapsed between the <code>PerformanceEntry</code> <code>startTime</code> and the reception of the first header.</li> </ul> <p>If <code>performanceEntry.name</code> is equal to <code>Http2Session</code>, the <code>detail</code> will contain the following properties:</p> <ul> <li><code>bytesRead</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of bytes received for this <code>Http2Session</code>.</li> <li><code>bytesWritten</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of bytes sent for this <code>Http2Session</code>.</li> <li><code>framesReceived</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of HTTP/2 frames received by the <code>Http2Session</code>.</li> <li><code>framesSent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of HTTP/2 frames sent by the <code>Http2Session</code>.</li> <li><code>maxConcurrentStreams</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The maximum number of streams concurrently open during the lifetime of the <code>Http2Session</code>.</li> <li><code>pingRTT</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of milliseconds elapsed since the transmission of a <code>PING</code> frame and the reception of its acknowledgment. Only present if a <code>PING</code> frame has been sent on the <code>Http2Session</code>.</li> <li><code>streamAverageDuration</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The average duration (in milliseconds) for all <code>Http2Stream</code> instances.</li> <li><code>streamCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of <code>Http2Stream</code> instances processed by the <code>Http2Session</code>.</li> <li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Either <code>'server'</code> or <code>'client'</code> to identify the type of <code>Http2Session</code>.</li> </ul> <h4>Timerify ('function') Details<span><a class="mark" href="#timerify-function-details" id="timerify-function-details">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_timerify_function_details"></a></h4> <p>When <code>performanceEntry.type</code> is equal to <code>'function'</code>, the <code>performanceEntry.detail</code> property will be an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> listing the input arguments to the timed function.</p> <h4>Net ('net') Details<span><a class="mark" href="#net-net-details" id="net-net-details">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_net_net_details"></a></h4> <p>When <code>performanceEntry.type</code> is equal to <code>'net'</code>, the <code>performanceEntry.detail</code> property will be an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> containing additional information.</p> <p>If <code>performanceEntry.name</code> is equal to <code>connect</code>, the <code>detail</code> will contain the following properties: <code>host</code>, <code>port</code>.</p> <h4>DNS ('dns') Details<span><a class="mark" href="#dns-dns-details" id="dns-dns-details">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_dns_dns_details"></a></h4> <p>When <code>performanceEntry.type</code> is equal to <code>'dns'</code>, the <code>performanceEntry.detail</code> property will be an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> containing additional information.</p> <p>If <code>performanceEntry.name</code> is equal to <code>lookup</code>, the <code>detail</code> will contain the following properties: <code>hostname</code>, <code>family</code>, <code>hints</code>, <code>verbatim</code>, <code>addresses</code>.</p> <p>If <code>performanceEntry.name</code> is equal to <code>lookupService</code>, the <code>detail</code> will contain the following properties: <code>host</code>, <code>port</code>, <code>hostname</code>, <code>service</code>.</p> <p>If <code>performanceEntry.name</code> is equal to <code>queryxxx</code> or <code>getHostByAddr</code>, the <code>detail</code> will contain the following properties: <code>host</code>, <code>ttl</code>, <code>result</code>. The value of <code>result</code> is same as the result of <code>queryxxx</code> or <code>getHostByAddr</code>.</p> </section><section><h3>Class: <code>PerformanceNodeTiming</code><span><a class="mark" href="#class-performancenodetiming" id="class-performancenodetiming">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_class_performancenodetiming"></a></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li>Extends: <a href="perf_hooks.html#class-performanceentry" class="type"><PerformanceEntry></a></li> </ul> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>Provides timing details for Node.js itself. The constructor of this class is not exposed to users.</p> <h4><code>performanceNodeTiming.bootstrapComplete</code><span><a class="mark" href="#performancenodetimingbootstrapcomplete" id="performancenodetimingbootstrapcomplete">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performancenodetiming_bootstrapcomplete"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp at which the Node.js process completed bootstrapping. If bootstrapping has not yet finished, the property has the value of -1.</p> <h4><code>performanceNodeTiming.environment</code><span><a class="mark" href="#performancenodetimingenvironment" id="performancenodetimingenvironment">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performancenodetiming_environment"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp at which the Node.js environment was initialized.</p> <h4><code>performanceNodeTiming.idleTime</code><span><a class="mark" href="#performancenodetimingidletime" id="performancenodetimingidletime">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performancenodetiming_idletime"></a></h4> <div class="api_metadata"> <span>Added in: v14.10.0, v12.19.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp of the amount of time the event loop has been idle within the event loop's event provider (e.g. <code>epoll_wait</code>). This does not take CPU usage into consideration. If the event loop has not yet started (e.g., in the first tick of the main script), the property has the value of 0.</p> <h4><code>performanceNodeTiming.loopExit</code><span><a class="mark" href="#performancenodetimingloopexit" id="performancenodetimingloopexit">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performancenodetiming_loopexit"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp at which the Node.js event loop exited. If the event loop has not yet exited, the property has the value of -1. It can only have a value of not -1 in a handler of the <a href="process.html#event-exit"><code>'exit'</code></a> event.</p> <h4><code>performanceNodeTiming.loopStart</code><span><a class="mark" href="#performancenodetimingloopstart" id="performancenodetimingloopstart">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performancenodetiming_loopstart"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp at which the Node.js event loop started. If the event loop has not yet started (e.g., in the first tick of the main script), the property has the value of -1.</p> <h4><code>performanceNodeTiming.nodeStart</code><span><a class="mark" href="#performancenodetimingnodestart" id="performancenodetimingnodestart">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performancenodetiming_nodestart"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp at which the Node.js process was initialized.</p> <h4><code>performanceNodeTiming.v8Start</code><span><a class="mark" href="#performancenodetimingv8start" id="performancenodetimingv8start">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performancenodetiming_v8start"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp at which the V8 platform was initialized.</p> </section><section><h3>Class: <code>PerformanceResourceTiming</code><span><a class="mark" href="#class-performanceresourcetiming" id="class-performanceresourcetiming">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_class_performanceresourcetiming"></a></h3> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li>Extends: <a href="perf_hooks.html#class-performanceentry" class="type"><PerformanceEntry></a></li> </ul> <p>Provides detailed network timing data regarding the loading of an application's resources.</p> <p>The constructor of this class is not exposed to users directly.</p> <h4><code>performanceResourceTiming.workerStart</code><span><a class="mark" href="#performanceresourcetimingworkerstart" id="performanceresourcetimingworkerstart">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_workerstart"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp at immediately before dispatching the <code>fetch</code> request. If the resource is not intercepted by a worker the property will always return 0.</p> <h4><code>performanceResourceTiming.redirectStart</code><span><a class="mark" href="#performanceresourcetimingredirectstart" id="performanceresourcetimingredirectstart">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_redirectstart"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp that represents the start time of the fetch which initiates the redirect.</p> <h4><code>performanceResourceTiming.redirectEnd</code><span><a class="mark" href="#performanceresourcetimingredirectend" id="performanceresourcetimingredirectend">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_redirectend"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp that will be created immediately after receiving the last byte of the response of the last redirect.</p> <h4><code>performanceResourceTiming.fetchStart</code><span><a class="mark" href="#performanceresourcetimingfetchstart" id="performanceresourcetimingfetchstart">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_fetchstart"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp immediately before the Node.js starts to fetch the resource.</p> <h4><code>performanceResourceTiming.domainLookupStart</code><span><a class="mark" href="#performanceresourcetimingdomainlookupstart" id="performanceresourcetimingdomainlookupstart">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_domainlookupstart"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp immediately before the Node.js starts the domain name lookup for the resource.</p> <h4><code>performanceResourceTiming.domainLookupEnd</code><span><a class="mark" href="#performanceresourcetimingdomainlookupend" id="performanceresourcetimingdomainlookupend">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_domainlookupend"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp representing the time immediately after the Node.js finished the domain name lookup for the resource.</p> <h4><code>performanceResourceTiming.connectStart</code><span><a class="mark" href="#performanceresourcetimingconnectstart" id="performanceresourcetimingconnectstart">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_connectstart"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp representing the time immediately before Node.js starts to establish the connection to the server to retrieve the resource.</p> <h4><code>performanceResourceTiming.connectEnd</code><span><a class="mark" href="#performanceresourcetimingconnectend" id="performanceresourcetimingconnectend">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_connectend"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp representing the time immediately after Node.js finishes establishing the connection to the server to retrieve the resource.</p> <h4><code>performanceResourceTiming.secureConnectionStart</code><span><a class="mark" href="#performanceresourcetimingsecureconnectionstart" id="performanceresourcetimingsecureconnectionstart">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_secureconnectionstart"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp representing the time immediately before Node.js starts the handshake process to secure the current connection.</p> <h4><code>performanceResourceTiming.requestStart</code><span><a class="mark" href="#performanceresourcetimingrequeststart" id="performanceresourcetimingrequeststart">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_requeststart"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp representing the time immediately before Node.js receives the first byte of the response from the server.</p> <h4><code>performanceResourceTiming.responseEnd</code><span><a class="mark" href="#performanceresourcetimingresponseend" id="performanceresourcetimingresponseend">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_responseend"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp representing the time immediately after Node.js receives the last byte of the resource or immediately before the transport connection is closed, whichever comes first.</p> <h4><code>performanceResourceTiming.transferSize</code><span><a class="mark" href="#performanceresourcetimingtransfersize" id="performanceresourcetimingtransfersize">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_transfersize"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>A number representing the size (in octets) of the fetched resource. The size includes the response header fields plus the response payload body.</p> <h4><code>performanceResourceTiming.encodedBodySize</code><span><a class="mark" href="#performanceresourcetimingencodedbodysize" id="performanceresourcetimingencodedbodysize">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_encodedbodysize"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>A number representing the size (in octets) received from the fetch (HTTP or cache), of the payload body, before removing any applied content-codings.</p> <h4><code>performanceResourceTiming.decodedBodySize</code><span><a class="mark" href="#performanceresourcetimingdecodedbodysize" id="performanceresourcetimingdecodedbodysize">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_decodedbodysize"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>A number representing the size (in octets) received from the fetch (HTTP or cache), of the message body, after removing any applied content-codings.</p> <h4><code>performanceResourceTiming.toJSON()</code><span><a class="mark" href="#performanceresourcetimingtojson" id="performanceresourcetimingtojson">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceresourcetiming_tojson"></a></h4> <div class="api_metadata"> <span>Added in: v16.17.0</span> </div> <p>Returns a <code>object</code> that is the JSON representation of the <code>PerformanceResourceTiming</code> object</p> </section><section><h3>Class: <code>perf_hooks.PerformanceObserver</code><span><a class="mark" href="#class-perf_hooksperformanceobserver" id="class-perf_hooksperformanceobserver">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_class_perf_hooks_performanceobserver"></a></h3> <h4><code>new PerformanceObserver(callback)</code><span><a class="mark" href="#new-performanceobservercallback" id="new-performanceobservercallback">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_new_performanceobserver_callback"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> <ul> <li><code>list</code> <a href="perf_hooks.html#class-performanceobserverentrylist" class="type"><PerformanceObserverEntryList></a></li> <li><code>observer</code> <a href="perf_hooks.html#class-perf_hooksperformanceobserver" class="type"><PerformanceObserver></a></li> </ul> </li> </ul> <p><code>PerformanceObserver</code> objects provide notifications when new <code>PerformanceEntry</code> instances have been added to the Performance Timeline.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { performance, <span class="hljs-title class_">PerformanceObserver</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">list, observer</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(list.<span class="hljs-title function_">getEntries</span>()); performance.<span class="hljs-title function_">clearMarks</span>(); performance.<span class="hljs-title function_">clearMeasures</span>(); observer.<span class="hljs-title function_">disconnect</span>(); }); obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'test'</span>);</code></pre> <p>Because <code>PerformanceObserver</code> instances introduce their own additional performance overhead, instances should not be left subscribed to notifications indefinitely. Users should disconnect observers as soon as they are no longer needed.</p> <p>The <code>callback</code> is invoked when a <code>PerformanceObserver</code> is notified about new <code>PerformanceEntry</code> instances. The callback receives a <code>PerformanceObserverEntryList</code> instance and a reference to the <code>PerformanceObserver</code>.</p> <h4><code>performanceObserver.disconnect()</code><span><a class="mark" href="#performanceobserverdisconnect" id="performanceobserverdisconnect">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceobserver_disconnect"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <p>Disconnects the <code>PerformanceObserver</code> instance from all notifications.</p> <h4><code>performanceObserver.observe(options)</code><span><a class="mark" href="#performanceobserverobserveoptions" id="performanceobserverobserveoptions">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceobserver_observe_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>v16.7.0</td> <td><p>Updated to conform to Performance Timeline Level 2. The buffered option has been added back.</p></td></tr> <tr><td>v16.0.0</td> <td><p>Updated to conform to User Timing Level 3. The buffered option has been removed.</p></td></tr> <tr><td>v8.5.0</td> <td><p><span>Added in: v8.5.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <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>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A single <a href="perf_hooks.html#class-performanceentry" class="type"><PerformanceEntry></a> type. Must not be given if <code>entryTypes</code> is already specified.</li> <li><code>entryTypes</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> An array of strings identifying the types of <a href="perf_hooks.html#class-performanceentry" class="type"><PerformanceEntry></a> instances the observer is interested in. If not provided an error will be thrown.</li> <li><code>buffered</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If true, the observer callback is called with a list global <code>PerformanceEntry</code> buffered entries. If false, only <code>PerformanceEntry</code>s created after the time point are sent to the observer callback. <strong>Default:</strong> <code>false</code>.</li> </ul> </li> </ul> <p>Subscribes the <a href="perf_hooks.html#class-perf_hooksperformanceobserver" class="type"><PerformanceObserver></a> instance to notifications of new <a href="perf_hooks.html#class-performanceentry" class="type"><PerformanceEntry></a> instances identified either by <code>options.entryTypes</code> or <code>options.type</code>:</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { performance, <span class="hljs-title class_">PerformanceObserver</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">list, observer</span>) =></span> { <span class="hljs-comment">// Called once asynchronously. `list` contains three items.</span> }); obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">type</span>: <span class="hljs-string">'mark'</span> }); <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> n = <span class="hljs-number">0</span>; n < <span class="hljs-number">3</span>; n++) performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">`test<span class="hljs-subst">${n}</span>`</span>);</code></pre> </section><section><h3>Class: <code>PerformanceObserverEntryList</code><span><a class="mark" href="#class-performanceobserverentrylist" id="class-performanceobserverentrylist">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_class_performanceobserverentrylist"></a></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <p>The <code>PerformanceObserverEntryList</code> class is used to provide access to the <code>PerformanceEntry</code> instances passed to a <code>PerformanceObserver</code>. The constructor of this class is not exposed to users.</p> <h4><code>performanceObserverEntryList.getEntries()</code><span><a class="mark" href="#performanceobserverentrylistgetentries" id="performanceobserverentrylistgetentries">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceobserverentrylist_getentries"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li>Returns: <a href="perf_hooks.html#class-performanceentry" class="type"><PerformanceEntry[]></a></li> </ul> <p>Returns a list of <code>PerformanceEntry</code> objects in chronological order with respect to <code>performanceEntry.startTime</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { performance, <span class="hljs-title class_">PerformanceObserver</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">perfObserverList, observer</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntries</span>()); <span class="hljs-comment">/** * [ * PerformanceEntry { * name: 'test', * entryType: 'mark', * startTime: 81.465639, * duration: 0 * }, * PerformanceEntry { * name: 'meow', * entryType: 'mark', * startTime: 81.860064, * duration: 0 * } * ] */</span> performance.<span class="hljs-title function_">clearMarks</span>(); performance.<span class="hljs-title function_">clearMeasures</span>(); observer.<span class="hljs-title function_">disconnect</span>(); }); obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">type</span>: <span class="hljs-string">'mark'</span> }); performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'test'</span>); performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'meow'</span>);</code></pre> <h4><code>performanceObserverEntryList.getEntriesByName(name[, type])</code><span><a class="mark" href="#performanceobserverentrylistgetentriesbynamename-type" id="performanceobserverentrylistgetentriesbynamename-type">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceobserverentrylist_getentriesbyname_name_type"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> <li><code>type</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="perf_hooks.html#class-performanceentry" class="type"><PerformanceEntry[]></a></li> </ul> <p>Returns a list of <code>PerformanceEntry</code> objects in chronological order with respect to <code>performanceEntry.startTime</code> whose <code>performanceEntry.name</code> is equal to <code>name</code>, and optionally, whose <code>performanceEntry.entryType</code> is equal to <code>type</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { performance, <span class="hljs-title class_">PerformanceObserver</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">perfObserverList, observer</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntriesByName</span>(<span class="hljs-string">'meow'</span>)); <span class="hljs-comment">/** * [ * PerformanceEntry { * name: 'meow', * entryType: 'mark', * startTime: 98.545991, * duration: 0 * } * ] */</span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntriesByName</span>(<span class="hljs-string">'nope'</span>)); <span class="hljs-comment">// []</span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntriesByName</span>(<span class="hljs-string">'test'</span>, <span class="hljs-string">'mark'</span>)); <span class="hljs-comment">/** * [ * PerformanceEntry { * name: 'test', * entryType: 'mark', * startTime: 63.518931, * duration: 0 * } * ] */</span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntriesByName</span>(<span class="hljs-string">'test'</span>, <span class="hljs-string">'measure'</span>)); <span class="hljs-comment">// []</span> performance.<span class="hljs-title function_">clearMarks</span>(); performance.<span class="hljs-title function_">clearMeasures</span>(); observer.<span class="hljs-title function_">disconnect</span>(); }); obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>, <span class="hljs-string">'measure'</span>] }); performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'test'</span>); performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'meow'</span>);</code></pre> <h4><code>performanceObserverEntryList.getEntriesByType(type)</code><span><a class="mark" href="#performanceobserverentrylistgetentriesbytypetype" id="performanceobserverentrylistgetentriesbytypetype">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_performanceobserverentrylist_getentriesbytype_type"></a></h4> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><code>type</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="perf_hooks.html#class-performanceentry" class="type"><PerformanceEntry[]></a></li> </ul> <p>Returns a list of <code>PerformanceEntry</code> objects in chronological order with respect to <code>performanceEntry.startTime</code> whose <code>performanceEntry.entryType</code> is equal to <code>type</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { performance, <span class="hljs-title class_">PerformanceObserver</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">perfObserverList, observer</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntriesByType</span>(<span class="hljs-string">'mark'</span>)); <span class="hljs-comment">/** * [ * PerformanceEntry { * name: 'test', * entryType: 'mark', * startTime: 55.897834, * duration: 0 * }, * PerformanceEntry { * name: 'meow', * entryType: 'mark', * startTime: 56.350146, * duration: 0 * } * ] */</span> performance.<span class="hljs-title function_">clearMarks</span>(); performance.<span class="hljs-title function_">clearMeasures</span>(); observer.<span class="hljs-title function_">disconnect</span>(); }); obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">type</span>: <span class="hljs-string">'mark'</span> }); performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'test'</span>); performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'meow'</span>);</code></pre> </section><section><h3><code>perf_hooks.createHistogram([options])</code><span><a class="mark" href="#perf_hookscreatehistogramoptions" id="perf_hookscreatehistogramoptions">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_perf_hooks_createhistogram_options"></a></h3> <div class="api_metadata"> <span>Added in: v15.9.0</span> </div> <ul> <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>lowest</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt" class="type"><bigint></a> The lowest discernible value. Must be an integer value greater than 0. <strong>Default:</strong> <code>1</code>.</li> <li><code>highest</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt" class="type"><bigint></a> The highest recordable value. Must be an integer value that is equal to or greater than two times <code>lowest</code>. <strong>Default:</strong> <code>Number.MAX_SAFE_INTEGER</code>.</li> <li><code>figures</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of accuracy digits. Must be a number between <code>1</code> and <code>5</code>. <strong>Default:</strong> <code>3</code>.</li> </ul> </li> <li>Returns <a href="perf_hooks.html#class-recordablehistogram-extends-histogram" class="type"><RecordableHistogram></a></li> </ul> <p>Returns a <a href="perf_hooks.html#class-recordablehistogram-extends-histogram" class="type"><RecordableHistogram></a>.</p> </section><section><h3><code>perf_hooks.monitorEventLoopDelay([options])</code><span><a class="mark" href="#perf_hooksmonitoreventloopdelayoptions" id="perf_hooksmonitoreventloopdelayoptions">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_perf_hooks_monitoreventloopdelay_options"></a></h3> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <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>resolution</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The sampling rate in milliseconds. Must be greater than zero. <strong>Default:</strong> <code>10</code>.</li> </ul> </li> <li>Returns: <a href="perf_hooks.html#class-intervalhistogram-extends-histogram" class="type"><IntervalHistogram></a></li> </ul> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>Creates an <code>IntervalHistogram</code> object that samples and reports the event loop delay over time. The delays will be reported in nanoseconds.</p> <p>Using a timer to detect approximate event loop delay works because the execution of timers is tied specifically to the lifecycle of the libuv event loop. That is, a delay in the loop will cause a delay in the execution of the timer, and those delays are specifically what this API is intended to detect.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { monitorEventLoopDelay } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">const</span> h = <span class="hljs-title function_">monitorEventLoopDelay</span>({ <span class="hljs-attr">resolution</span>: <span class="hljs-number">20</span> }); h.<span class="hljs-title function_">enable</span>(); <span class="hljs-comment">// Do something.</span> h.<span class="hljs-title function_">disable</span>(); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">min</span>); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">max</span>); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">mean</span>); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">stddev</span>); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">percentiles</span>); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-title function_">percentile</span>(<span class="hljs-number">50</span>)); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-title function_">percentile</span>(<span class="hljs-number">99</span>));</code></pre> </section><section><h3>Class: <code>Histogram</code><span><a class="mark" href="#class-histogram" id="class-histogram">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_class_histogram"></a></h3> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <h4><code>histogram.count</code><span><a class="mark" href="#histogramcount" id="histogramcount">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_count"></a></h4> <div class="api_metadata"> <span>Added in: v16.14.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The number of samples recorded by the histogram.</p> <h4><code>histogram.countBigInt</code><span><a class="mark" href="#histogramcountbigint" id="histogramcountbigint">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_countbigint"></a></h4> <div class="api_metadata"> <span>Added in: v16.14.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt" class="type"><bigint></a></li> </ul> <p>The number of samples recorded by the histogram.</p> <h4><code>histogram.exceeds</code><span><a class="mark" href="#histogramexceeds" id="histogramexceeds">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_exceeds"></a></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold.</p> <h4><code>histogram.exceedsBigInt</code><span><a class="mark" href="#histogramexceedsbigint" id="histogramexceedsbigint">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_exceedsbigint"></a></h4> <div class="api_metadata"> <span>Added in: v16.14.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt" class="type"><bigint></a></li> </ul> <p>The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold.</p> <h4><code>histogram.max</code><span><a class="mark" href="#histogrammax" id="histogrammax">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_max"></a></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The maximum recorded event loop delay.</p> <h4><code>histogram.maxBigInt</code><span><a class="mark" href="#histogrammaxbigint" id="histogrammaxbigint">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_maxbigint"></a></h4> <div class="api_metadata"> <span>Added in: v16.14.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt" class="type"><bigint></a></li> </ul> <p>The maximum recorded event loop delay.</p> <h4><code>histogram.mean</code><span><a class="mark" href="#histogrammean" id="histogrammean">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_mean"></a></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The mean of the recorded event loop delays.</p> <h4><code>histogram.min</code><span><a class="mark" href="#histogrammin" id="histogrammin">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_min"></a></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The minimum recorded event loop delay.</p> <h4><code>histogram.minBigInt</code><span><a class="mark" href="#histogramminbigint" id="histogramminbigint">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_minbigint"></a></h4> <div class="api_metadata"> <span>Added in: v16.14.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt" class="type"><bigint></a></li> </ul> <p>The minimum recorded event loop delay.</p> <h4><code>histogram.percentile(percentile)</code><span><a class="mark" href="#histogrampercentilepercentile" id="histogrampercentilepercentile">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_percentile_percentile"></a></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><code>percentile</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> A percentile value in the range (0, 100].</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>Returns the value at the given percentile.</p> <h4><code>histogram.percentileBigInt(percentile)</code><span><a class="mark" href="#histogrampercentilebigintpercentile" id="histogrampercentilebigintpercentile">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_percentilebigint_percentile"></a></h4> <div class="api_metadata"> <span>Added in: v16.14.0</span> </div> <ul> <li><code>percentile</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> A percentile value in the range (0, 100].</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt" class="type"><bigint></a></li> </ul> <p>Returns the value at the given percentile.</p> <h4><code>histogram.percentiles</code><span><a class="mark" href="#histogrampercentiles" id="histogrampercentiles">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_percentiles"></a></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map" class="type"><Map></a></li> </ul> <p>Returns a <code>Map</code> object detailing the accumulated percentile distribution.</p> <h4><code>histogram.percentilesBigInt</code><span><a class="mark" href="#histogrampercentilesbigint" id="histogrampercentilesbigint">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_percentilesbigint"></a></h4> <div class="api_metadata"> <span>Added in: v16.14.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map" class="type"><Map></a></li> </ul> <p>Returns a <code>Map</code> object detailing the accumulated percentile distribution.</p> <h4><code>histogram.reset()</code><span><a class="mark" href="#histogramreset" id="histogramreset">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_reset"></a></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <p>Resets the collected histogram data.</p> <h4><code>histogram.stddev</code><span><a class="mark" href="#histogramstddev" id="histogramstddev">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_stddev"></a></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The standard deviation of the recorded event loop delays.</p> </section><section><h3>Class: <code>IntervalHistogram extends Histogram</code><span><a class="mark" href="#class-intervalhistogram-extends-histogram" id="class-intervalhistogram-extends-histogram">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_class_intervalhistogram_extends_histogram"></a></h3> <p>A <code>Histogram</code> that is periodically updated on a given interval.</p> <h4><code>histogram.disable()</code><span><a class="mark" href="#histogramdisable" id="histogramdisable">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_disable"></a></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Disables the update interval timer. Returns <code>true</code> if the timer was stopped, <code>false</code> if it was already stopped.</p> <h4><code>histogram.enable()</code><span><a class="mark" href="#histogramenable" id="histogramenable">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_enable"></a></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Enables the update interval timer. Returns <code>true</code> if the timer was started, <code>false</code> if it was already started.</p> <h4>Cloning an <code>IntervalHistogram</code><span><a class="mark" href="#cloning-an-intervalhistogram" id="cloning-an-intervalhistogram">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_cloning_an_intervalhistogram"></a></h4> <p><a href="perf_hooks.html#class-intervalhistogram-extends-histogram" class="type"><IntervalHistogram></a> instances can be cloned via <a href="worker_threads.html#class-messageport" class="type"><MessagePort></a>. On the receiving end, the histogram is cloned as a plain <a href="perf_hooks.html#class-histogram" class="type"><Histogram></a> object that does not implement the <code>enable()</code> and <code>disable()</code> methods.</p> </section><section><h3>Class: <code>RecordableHistogram extends Histogram</code><span><a class="mark" href="#class-recordablehistogram-extends-histogram" id="class-recordablehistogram-extends-histogram">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_class_recordablehistogram_extends_histogram"></a></h3> <div class="api_metadata"> <span>Added in: v15.9.0</span> </div> <h4><code>histogram.add(other)</code><span><a class="mark" href="#histogramaddother" id="histogramaddother">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_add_other"></a></h4> <div class="api_metadata"> <span>Added in: v16.14.0</span> </div> <ul> <li><code>other</code> <a href="perf_hooks.html#class-recordablehistogram-extends-histogram" class="type"><RecordableHistogram></a></li> </ul> <p>Adds the values from <code>other</code> to this histogram.</p> <h4><code>histogram.record(val)</code><span><a class="mark" href="#histogramrecordval" id="histogramrecordval">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_record_val"></a></h4> <div class="api_metadata"> <span>Added in: v15.9.0</span> </div> <ul> <li><code>val</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt" class="type"><bigint></a> The amount to record in the histogram.</li> </ul> <h4><code>histogram.recordDelta()</code><span><a class="mark" href="#histogramrecorddelta" id="histogramrecorddelta">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_histogram_recorddelta"></a></h4> <div class="api_metadata"> <span>Added in: v15.9.0</span> </div> <p>Calculates the amount of time (in nanoseconds) that has passed since the previous call to <code>recordDelta()</code> and records that amount in the histogram.</p> </section><section><h3>Examples<span><a class="mark" href="#examples" id="examples">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_examples"></a></h3> <h4>Measuring the duration of async operations<span><a class="mark" href="#measuring-the-duration-of-async-operations" id="measuring-the-duration-of-async-operations">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_measuring_the_duration_of_async_operations"></a></h4> <p>The following example uses the <a href="async_hooks.html">Async Hooks</a> and Performance APIs to measure the actual duration of a Timeout operation (including the amount of time it took to execute the callback).</p> <pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; <span class="hljs-keyword">const</span> async_hooks = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); <span class="hljs-keyword">const</span> { performance, <span class="hljs-title class_">PerformanceObserver</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">const</span> set = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Set</span>(); <span class="hljs-keyword">const</span> hook = async_hooks.<span class="hljs-title function_">createHook</span>({ <span class="hljs-title function_">init</span>(<span class="hljs-params">id, type</span>) { <span class="hljs-keyword">if</span> (type === <span class="hljs-string">'Timeout'</span>) { performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Init`</span>); set.<span class="hljs-title function_">add</span>(id); } }, <span class="hljs-title function_">destroy</span>(<span class="hljs-params">id</span>) { <span class="hljs-keyword">if</span> (set.<span class="hljs-title function_">has</span>(id)) { set.<span class="hljs-title function_">delete</span>(id); performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Destroy`</span>); performance.<span class="hljs-title function_">measure</span>(<span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>`</span>, <span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Init`</span>, <span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Destroy`</span>); } } }); hook.<span class="hljs-title function_">enable</span>(); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">list, observer</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(list.<span class="hljs-title function_">getEntries</span>()[<span class="hljs-number">0</span>]); performance.<span class="hljs-title function_">clearMarks</span>(); performance.<span class="hljs-title function_">clearMeasures</span>(); observer.<span class="hljs-title function_">disconnect</span>(); }); obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'measure'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> {}, <span class="hljs-number">1000</span>);</code></pre> <h4>Measuring how long it takes to load dependencies<span><a class="mark" href="#measuring-how-long-it-takes-to-load-dependencies" id="measuring-how-long-it-takes-to-load-dependencies">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_measuring_how_long_it_takes_to_load_dependencies"></a></h4> <p>The following example measures the duration of <code>require()</code> operations to load dependencies:</p> <!-- eslint-disable no-global-assign --> <pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; <span class="hljs-keyword">const</span> { performance, <span class="hljs-title class_">PerformanceObserver</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">const</span> mod = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:module'</span>); <span class="hljs-comment">// Monkey patch the require function</span> mod.<span class="hljs-property">Module</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>.<span class="hljs-property">require</span> = performance.<span class="hljs-title function_">timerify</span>(mod.<span class="hljs-property">Module</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>.<span class="hljs-property">require</span>); <span class="hljs-built_in">require</span> = performance.<span class="hljs-title function_">timerify</span>(<span class="hljs-built_in">require</span>); <span class="hljs-comment">// Activate the observer</span> <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">list</span>) =></span> { <span class="hljs-keyword">const</span> entries = list.<span class="hljs-title function_">getEntries</span>(); entries.<span class="hljs-title function_">forEach</span>(<span class="hljs-function">(<span class="hljs-params">entry</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`require('<span class="hljs-subst">${entry[<span class="hljs-number">0</span>]}</span>')`</span>, entry.<span class="hljs-property">duration</span>); }); performance.<span class="hljs-title function_">clearMarks</span>(); performance.<span class="hljs-title function_">clearMeasures</span>(); obs.<span class="hljs-title function_">disconnect</span>(); }); obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'function'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); <span class="hljs-built_in">require</span>(<span class="hljs-string">'some-module'</span>);</code></pre> <h4>Measuring how long one HTTP round-trip takes<span><a class="mark" href="#measuring-how-long-one-http-round-trip-takes" id="measuring-how-long-one-http-round-trip-takes">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_measuring_how_long_one_http_round_trip_takes"></a></h4> <p>The following example is used to trace the time spent by HTTP client (<code>OutgoingMessage</code>) and HTTP request (<code>IncomingMessage</code>). For HTTP client, it means the time interval between starting the request and receiving the response, and for HTTP request, it means the time interval between receiving the request and sending the response:</p> <pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; <span class="hljs-keyword">const</span> { <span class="hljs-title class_">PerformanceObserver</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">const</span> http = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:http'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">items</span>) =></span> { items.<span class="hljs-title function_">getEntries</span>().<span class="hljs-title function_">forEach</span>(<span class="hljs-function">(<span class="hljs-params">item</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(item); }); }); obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'http'</span>] }); <span class="hljs-keyword">const</span> <span class="hljs-variable constant_">PORT</span> = <span class="hljs-number">8080</span>; http.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { res.<span class="hljs-title function_">end</span>(<span class="hljs-string">'ok'</span>); }).<span class="hljs-title function_">listen</span>(<span class="hljs-variable constant_">PORT</span>, <span class="hljs-function">() =></span> { http.<span class="hljs-title function_">get</span>(<span class="hljs-string">`http://127.0.0.1:<span class="hljs-subst">${PORT}</span>`</span>); });</code></pre> <h4>Measuring how long the <code>net.connect</code> (only for TCP) takes when the connection is successful<span><a class="mark" href="#measuring-how-long-the-netconnect-only-for-tcp-takes-when-the-connection-is-successful" id="measuring-how-long-the-netconnect-only-for-tcp-takes-when-the-connection-is-successful">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_measuring_how_long_the_net_connect_only_for_tcp_takes_when_the_connection_is_successful"></a></h4> <pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; <span class="hljs-keyword">const</span> { <span class="hljs-title class_">PerformanceObserver</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">const</span> net = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:net'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">items</span>) =></span> { items.<span class="hljs-title function_">getEntries</span>().<span class="hljs-title function_">forEach</span>(<span class="hljs-function">(<span class="hljs-params">item</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(item); }); }); obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'net'</span>] }); <span class="hljs-keyword">const</span> <span class="hljs-variable constant_">PORT</span> = <span class="hljs-number">8080</span>; net.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">socket</span>) =></span> { socket.<span class="hljs-title function_">destroy</span>(); }).<span class="hljs-title function_">listen</span>(<span class="hljs-variable constant_">PORT</span>, <span class="hljs-function">() =></span> { net.<span class="hljs-title function_">connect</span>(<span class="hljs-variable constant_">PORT</span>); });</code></pre> <h4>Measuring how long the DNS takes when the request is successful<span><a class="mark" href="#measuring-how-long-the-dns-takes-when-the-request-is-successful" id="measuring-how-long-the-dns-takes-when-the-request-is-successful">#</a></span><a aria-hidden="true" class="legacy" id="perf_hooks_measuring_how_long_the_dns_takes_when_the_request_is_successful"></a></h4> <pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; <span class="hljs-keyword">const</span> { <span class="hljs-title class_">PerformanceObserver</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:perf_hooks'</span>); <span class="hljs-keyword">const</span> dns = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:dns'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">items</span>) =></span> { items.<span class="hljs-title function_">getEntries</span>().<span class="hljs-title function_">forEach</span>(<span class="hljs-function">(<span class="hljs-params">item</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(item); }); }); obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'dns'</span>] }); dns.<span class="hljs-title function_">lookup</span>(<span class="hljs-string">'localhost'</span>, <span class="hljs-function">() =></span> {}); dns.<span class="hljs-property">promises</span>.<span class="hljs-title function_">resolve</span>(<span class="hljs-string">'localhost'</span>);</code></pre></section> <!-- API END --> </div> </div> </div> </body> </html>