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<b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v17.x/api/embedding.html">17.x</a></li> <li><a href="https://nodejs.org/docs/latest-v16.x/api/embedding.html">16.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v15.x/api/embedding.html">15.x</a></li> <li><a href="https://nodejs.org/docs/latest-v14.x/api/embedding.html">14.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v13.x/api/embedding.html">13.x</a></li> <li><a href="https://nodejs.org/docs/latest-v12.x/api/embedding.html">12.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="embedding.json">View as JSON</a> </li> <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/embedding.md">Edit on GitHub</a></li> </ul> </div> </li> </ul> </div> <hr> </header> <details id="toc" open><summary>Table of contents</summary><ul> <li><a href="#c-embedder-api">C++ embedder API</a> <ul> <li><a href="#example-embedding-application">Example embedding application</a> <ul> <li><a href="#setting-up-per-process-state">Setting up per-process state</a></li> <li><a href="#per-instance-state">Per-instance state</a></li> </ul> </li> </ul> </li> </ul></details> <div id="apicontent"> <h2>C++ embedder API<span><a class="mark" href="#c-embedder-api" id="c-embedder-api">#</a></span><a aria-hidden="true" class="legacy" id="embedding_c_embedder_api"></a></h2> <p>Node.js provides a number of C++ APIs that can be used to execute JavaScript in a Node.js environment from other C++ software.</p> <p>The documentation for these APIs can be found in <a href="https://github.com/nodejs/node/blob/HEAD/src/node.h">src/node.h</a> in the Node.js source tree. In addition to the APIs exposed by Node.js, some required concepts are provided by the V8 embedder API.</p> <p>Because using Node.js as an embedded library is different from writing code that is executed by Node.js, breaking changes do not follow typical Node.js <a href="deprecations.html">deprecation policy</a> and may occur on each semver-major release without prior warning.</p> <section><h3>Example embedding application<span><a class="mark" href="#example-embedding-application" id="example-embedding-application">#</a></span><a aria-hidden="true" class="legacy" id="embedding_example_embedding_application"></a></h3> <p>The following sections will provide an overview over how to use these APIs to create an application from scratch that will perform the equivalent of <code>node -e <code></code>, i.e. that will take a piece of JavaScript and run it in a Node.js-specific environment.</p> <p>The full code can be found <a href="https://github.com/nodejs/node/blob/HEAD/test/embedding/embedtest.cc">in the Node.js source tree</a>.</p> <h4>Setting up per-process state<span><a class="mark" href="#setting-up-per-process-state" id="setting-up-per-process-state">#</a></span><a aria-hidden="true" class="legacy" id="embedding_setting_up_per_process_state"></a></h4> <p>Node.js requires some per-process state management in order to run:</p> <ul> <li>Arguments parsing for Node.js <a href="cli.html">CLI options</a>,</li> <li>V8 per-process requirements, such as a <code>v8::Platform</code> instance.</li> </ul> <p>The following example shows how these can be set up. Some class names are from the <code>node</code> and <code>v8</code> C++ namespaces, respectively.</p> <pre><code class="language-cpp"><span class="hljs-function"><span class="hljs-type">int</span> <span class="hljs-title">main</span><span class="hljs-params">(<span class="hljs-type">int</span> argc, <span class="hljs-type">char</span>** argv)</span> </span>{ argv = <span class="hljs-built_in">uv_setup_args</span>(argc, argv); <span class="hljs-function">std::vector<std::string> <span class="hljs-title">args</span><span class="hljs-params">(argv, argv + argc)</span></span>; std::vector<std::string> exec_args; std::vector<std::string> errors; <span class="hljs-comment">// Parse Node.js CLI options, and print any errors that have occurred while</span> <span class="hljs-comment">// trying to parse them.</span> <span class="hljs-type">int</span> exit_code = node::<span class="hljs-built_in">InitializeNodeWithArgs</span>(&args, &exec_args, &errors); <span class="hljs-keyword">for</span> (<span class="hljs-type">const</span> std::string& error : errors) <span class="hljs-built_in">fprintf</span>(stderr, <span class="hljs-string">"%s: %s\n"</span>, args[<span class="hljs-number">0</span>].<span class="hljs-built_in">c_str</span>(), error.<span class="hljs-built_in">c_str</span>()); <span class="hljs-keyword">if</span> (exit_code != <span class="hljs-number">0</span>) { <span class="hljs-keyword">return</span> exit_code; } <span class="hljs-comment">// Create a v8::Platform instance. `MultiIsolatePlatform::Create()` is a way</span> <span class="hljs-comment">// to create a v8::Platform instance that Node.js can use when creating</span> <span class="hljs-comment">// Worker threads. When no `MultiIsolatePlatform` instance is present,</span> <span class="hljs-comment">// Worker threads are disabled.</span> std::unique_ptr<MultiIsolatePlatform> platform = MultiIsolatePlatform::<span class="hljs-built_in">Create</span>(<span class="hljs-number">4</span>); V8::<span class="hljs-built_in">InitializePlatform</span>(platform.<span class="hljs-built_in">get</span>()); V8::<span class="hljs-built_in">Initialize</span>(); <span class="hljs-comment">// See below for the contents of this function.</span> <span class="hljs-type">int</span> ret = <span class="hljs-built_in">RunNodeInstance</span>(platform.<span class="hljs-built_in">get</span>(), args, exec_args); V8::<span class="hljs-built_in">Dispose</span>(); V8::<span class="hljs-built_in">ShutdownPlatform</span>(); <span class="hljs-keyword">return</span> ret; }</code></pre> <h4>Per-instance state<span><a class="mark" href="#per-instance-state" id="per-instance-state">#</a></span><a aria-hidden="true" class="legacy" id="embedding_per_instance_state"></a></h4> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v15.0.0</td> <td><p>The <code>CommonEnvironmentSetup</code> and <code>SpinEventLoop</code> utilities were added.</p></td></tr> </tbody></table> </details> </div> <p>Node.js has a concept of a “Node.js instance”, that is commonly being referred to as <code>node::Environment</code>. Each <code>node::Environment</code> is associated with:</p> <ul> <li>Exactly one <code>v8::Isolate</code>, i.e. one JS Engine instance,</li> <li>Exactly one <code>uv_loop_t</code>, i.e. one event loop, and</li> <li>A number of <code>v8::Context</code>s, but exactly one main <code>v8::Context</code>.</li> <li>One <code>node::IsolateData</code> instance that contains information that could be shared by multiple <code>node::Environment</code>s that use the same <code>v8::Isolate</code>. Currently, no testing if performed for this scenario.</li> </ul> <p>In order to set up a <code>v8::Isolate</code>, an <code>v8::ArrayBuffer::Allocator</code> needs to be provided. One possible choice is the default Node.js allocator, which can be created through <code>node::ArrayBufferAllocator::Create()</code>. Using the Node.js allocator allows minor performance optimizations when addons use the Node.js C++ <code>Buffer</code> API, and is required in order to track <code>ArrayBuffer</code> memory in <a href="process.html#processmemoryusage"><code>process.memoryUsage()</code></a>.</p> <p>Additionally, each <code>v8::Isolate</code> that is used for a Node.js instance needs to be registered and unregistered with the <code>MultiIsolatePlatform</code> instance, if one is being used, in order for the platform to know which event loop to use for tasks scheduled by the <code>v8::Isolate</code>.</p> <p>The <code>node::NewIsolate()</code> helper function creates a <code>v8::Isolate</code>, sets it up with some Node.js-specific hooks (e.g. the Node.js error handler), and registers it with the platform automatically.</p> <pre><code class="language-cpp"><span class="hljs-function"><span class="hljs-type">int</span> <span class="hljs-title">RunNodeInstance</span><span class="hljs-params">(MultiIsolatePlatform* platform, <span class="hljs-type">const</span> std::vector<std::string>& args, <span class="hljs-type">const</span> std::vector<std::string>& exec_args)</span> </span>{ <span class="hljs-type">int</span> exit_code = <span class="hljs-number">0</span>; <span class="hljs-comment">// Setup up a libuv event loop, v8::Isolate, and Node.js Environment.</span> std::vector<std::string> errors; std::unique_ptr<CommonEnvironmentSetup> setup = CommonEnvironmentSetup::<span class="hljs-built_in">Create</span>(platform, &errors, args, exec_args); <span class="hljs-keyword">if</span> (!setup) { <span class="hljs-keyword">for</span> (<span class="hljs-type">const</span> std::string& err : errors) <span class="hljs-built_in">fprintf</span>(stderr, <span class="hljs-string">"%s: %s\n"</span>, args[<span class="hljs-number">0</span>].<span class="hljs-built_in">c_str</span>(), err.<span class="hljs-built_in">c_str</span>()); <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; } Isolate* isolate = setup-><span class="hljs-built_in">isolate</span>(); Environment* env = setup-><span class="hljs-built_in">env</span>(); { <span class="hljs-function">Locker <span class="hljs-title">locker</span><span class="hljs-params">(isolate)</span></span>; <span class="hljs-function">Isolate::Scope <span class="hljs-title">isolate_scope</span><span class="hljs-params">(isolate)</span></span>; <span class="hljs-function">HandleScope <span class="hljs-title">handle_scope</span><span class="hljs-params">(isolate)</span></span>; <span class="hljs-comment">// The v8::Context needs to be entered when node::CreateEnvironment() and</span> <span class="hljs-comment">// node::LoadEnvironment() are being called.</span> <span class="hljs-function">Context::Scope <span class="hljs-title">context_scope</span><span class="hljs-params">(setup->context())</span></span>; <span class="hljs-comment">// Set up the Node.js instance for execution, and run code inside of it.</span> <span class="hljs-comment">// There is also a variant that takes a callback and provides it with</span> <span class="hljs-comment">// the `require` and `process` objects, so that it can manually compile</span> <span class="hljs-comment">// and run scripts as needed.</span> <span class="hljs-comment">// The `require` function inside this script does *not* access the file</span> <span class="hljs-comment">// system, and can only load built-in Node.js modules.</span> <span class="hljs-comment">// `module.createRequire()` is being used to create one that is able to</span> <span class="hljs-comment">// load files from the disk, and uses the standard CommonJS file loader</span> <span class="hljs-comment">// instead of the internal-only `require` function.</span> MaybeLocal<Value> loadenv_ret = node::<span class="hljs-built_in">LoadEnvironment</span>( env, <span class="hljs-string">"const publicRequire ="</span> <span class="hljs-string">" require('node:module').createRequire(process.cwd() + '/');"</span> <span class="hljs-string">"globalThis.require = publicRequire;"</span> <span class="hljs-string">"require('node:vm').runInThisContext(process.argv[1]);"</span>); <span class="hljs-keyword">if</span> (loadenv_ret.<span class="hljs-built_in">IsEmpty</span>()) <span class="hljs-comment">// There has been a JS exception.</span> <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; exit_code = node::<span class="hljs-built_in">SpinEventLoop</span>(env).<span class="hljs-built_in">FromMaybe</span>(<span class="hljs-number">1</span>); <span class="hljs-comment">// node::Stop() can be used to explicitly stop the event loop and keep</span> <span class="hljs-comment">// further JavaScript from running. It can be called from any thread,</span> <span class="hljs-comment">// and will act like worker.terminate() if called from another thread.</span> node::<span class="hljs-built_in">Stop</span>(env); } <span class="hljs-keyword">return</span> exit_code; }</code></pre></section> <!-- API END --> </div> </div> </div> </body> </html>