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data-id="embedding" class="interior"> 90 <header> 91 <div class="header-container"> 92 <h1>Node.js v14.20.1 documentation</h1> 93 <button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" aria-label="Toggle dark mode/light mode" hidden> 94 <svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24"> 95 <path fill="none" d="M0 0h24v24H0z" /> 96 <path d="M11.1 12.08c-2.33-4.51-.5-8.48.53-10.07C6.27 2.2 1.98 6.59 1.98 12c0 .14.02.28.02.42.62-.27 1.29-.42 2-.42 1.66 0 3.18.83 4.1 2.15A4.01 4.01 0 0111 18c0 1.52-.87 2.83-2.12 3.51.98.32 2.03.5 3.11.5 3.5 0 6.58-1.8 8.37-4.52-2.36.23-6.98-.97-9.26-5.41z"/> 97 <path d="M7 16h-.18C6.4 14.84 5.3 14 4 14c-1.66 0-3 1.34-3 3s1.34 3 3 3h3c1.1 0 2-.9 2-2s-.9-2-2-2z"/> 98 </svg> 99 <svg xmlns="http://www.w3.org/2000/svg" class="icon light-icon" height="24" width="24"> 100 <path d="M0 0h24v24H0z" fill="none" /> 101 <path d="M6.76 4.84l-1.8-1.79-1.41 1.41 1.79 1.79 1.42-1.41zM4 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href="https://nodejs.org/docs/latest-v15.x/api/embedding.html">15.x</a></li> 123<li><a href="https://nodejs.org/docs/latest-v14.x/api/embedding.html">14.x <b>LTS</b></a></li></ol> 124 </li> 125 126 <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/embedding.md">Edit on GitHub</a></li> 127 </ul> 128 </div> 129 <hr> 130 </header> 131 132 <details id="toc" open><summary>Table of contents</summary><ul> 133<li><a href="#embedding_c_embedder_api">C++ embedder API</a> 134<ul> 135<li><a href="#embedding_example_embedding_application">Example embedding application</a> 136<ul> 137<li><a href="#embedding_setting_up_per_process_state">Setting up per-process state</a></li> 138<li><a href="#embedding_per_instance_state">Per-instance state</a></li> 139</ul> 140</li> 141</ul> 142</li> 143</ul></details> 144 145 <div id="apicontent"> 146 <h2>C++ embedder API<span><a class="mark" href="#embedding_c_embedder_api" id="embedding_c_embedder_api">#</a></span></h2> 147 148<p>Node.js provides a number of C++ APIs that can be used to execute JavaScript 149in a Node.js environment from other C++ software.</p> 150<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 151source tree. In addition to the APIs exposed by Node.js, some required concepts 152are provided by the V8 embedder API.</p> 153<p>Because using Node.js as an embedded library is different from writing code 154that is executed by Node.js, breaking changes do not follow typical Node.js 155<a href="deprecations.html">deprecation policy</a> and may occur on each semver-major release without prior 156warning.</p> 157<section><h3>Example embedding application<span><a class="mark" href="#embedding_example_embedding_application" id="embedding_example_embedding_application">#</a></span></h3> 158<p>The following sections will provide an overview over how to use these APIs 159to create an application from scratch that will perform the equivalent of 160<code>node -e <code></code>, i.e. that will take a piece of JavaScript and run it in 161a Node.js-specific environment.</p> 162<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> 163<h4>Setting up per-process state<span><a class="mark" href="#embedding_setting_up_per_process_state" id="embedding_setting_up_per_process_state">#</a></span></h4> 164<p>Node.js requires some per-process state management in order to run:</p> 165<ul> 166<li>Arguments parsing for Node.js <a href="cli.html">CLI options</a>,</li> 167<li>V8 per-process requirements, such as a <code>v8::Platform</code> instance.</li> 168</ul> 169<p>The following example shows how these can be set up. Some class names are from 170the <code>node</code> and <code>v8</code> C++ namespaces, respectively.</p> 171<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>{ 172 argv = <span class="hljs-built_in">uv_setup_args</span>(argc, argv); 173 <span class="hljs-function">std::vector<std::string> <span class="hljs-title">args</span><span class="hljs-params">(argv, argv + argc)</span></span>; 174 std::vector<std::string> exec_args; 175 std::vector<std::string> errors; 176 <span class="hljs-comment">// Parse Node.js CLI options, and print any errors that have occurred while</span> 177 <span class="hljs-comment">// trying to parse them.</span> 178 <span class="hljs-type">int</span> exit_code = node::<span class="hljs-built_in">InitializeNodeWithArgs</span>(&args, &exec_args, &errors); 179 <span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> std::string& error : errors) 180 <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>()); 181 <span class="hljs-keyword">if</span> (exit_code != <span class="hljs-number">0</span>) { 182 <span class="hljs-keyword">return</span> exit_code; 183 } 184 185 <span class="hljs-comment">// Create a v8::Platform instance. `MultiIsolatePlatform::Create()` is a way</span> 186 <span class="hljs-comment">// to create a v8::Platform instance that Node.js can use when creating</span> 187 <span class="hljs-comment">// Worker threads. When no `MultiIsolatePlatform` instance is present,</span> 188 <span class="hljs-comment">// Worker threads are disabled.</span> 189 std::unique_ptr<MultiIsolatePlatform> platform = 190 MultiIsolatePlatform::<span class="hljs-built_in">Create</span>(<span class="hljs-number">4</span>); 191 V8::<span class="hljs-built_in">InitializePlatform</span>(platform.<span class="hljs-built_in">get</span>()); 192 V8::<span class="hljs-built_in">Initialize</span>(); 193 194 <span class="hljs-comment">// See below for the contents of this function.</span> 195 <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); 196 197 V8::<span class="hljs-built_in">Dispose</span>(); 198 V8::<span class="hljs-built_in">ShutdownPlatform</span>(); 199 <span class="hljs-keyword">return</span> ret; 200}</code></pre> 201<h4>Per-instance state<span><a class="mark" href="#embedding_per_instance_state" id="embedding_per_instance_state">#</a></span></h4> 202<p>Node.js has a concept of a “Node.js instance”, that is commonly being referred 203to as <code>node::Environment</code>. Each <code>node::Environment</code> is associated with:</p> 204<ul> 205<li>Exactly one <code>v8::Isolate</code>, i.e. one JS Engine instance,</li> 206<li>Exactly one <code>uv_loop_t</code>, i.e. one event loop, and</li> 207<li>A number of <code>v8::Context</code>s, but exactly one main <code>v8::Context</code>.</li> 208<li>One <code>node::IsolateData</code> instance that contains information that could be 209shared by multiple <code>node::Environment</code>s that use the same <code>v8::Isolate</code>. 210Currently, no testing if performed for this scenario.</li> 211</ul> 212<p>In order to set up a <code>v8::Isolate</code>, an <code>v8::ArrayBuffer::Allocator</code> needs 213to be provided. One possible choice is the default Node.js allocator, which 214can be created through <code>node::ArrayBufferAllocator::Create()</code>. Using the Node.js 215allocator allows minor performance optimizations when addons use the Node.js 216C++ <code>Buffer</code> API, and is required in order to track <code>ArrayBuffer</code> memory in 217<a href="process.html#process_process_memoryusage"><code>process.memoryUsage()</code></a>.</p> 218<p>Additionally, each <code>v8::Isolate</code> that is used for a Node.js instance needs to 219be registered and unregistered with the <code>MultiIsolatePlatform</code> instance, if one 220is being used, in order for the platform to know which event loop to use 221for tasks scheduled by the <code>v8::Isolate</code>.</p> 222<p>The <code>node::NewIsolate()</code> helper function creates a <code>v8::Isolate</code>, 223sets it up with some Node.js-specific hooks (e.g. the Node.js error handler), 224and registers it with the platform automatically.</p> 225<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, 226 <span class="hljs-keyword">const</span> std::vector<std::string>& args, 227 <span class="hljs-keyword">const</span> std::vector<std::string>& exec_args)</span> </span>{ 228 <span class="hljs-type">int</span> exit_code = <span class="hljs-number">0</span>; 229 <span class="hljs-comment">// Set up a libuv event loop.</span> 230 <span class="hljs-type">uv_loop_t</span> loop; 231 <span class="hljs-type">int</span> ret = <span class="hljs-built_in">uv_loop_init</span>(&loop); 232 <span class="hljs-keyword">if</span> (ret != <span class="hljs-number">0</span>) { 233 <span class="hljs-built_in">fprintf</span>(stderr, <span class="hljs-string">"%s: Failed to initialize loop: %s\n"</span>, 234 args[<span class="hljs-number">0</span>].<span class="hljs-built_in">c_str</span>(), 235 <span class="hljs-built_in">uv_err_name</span>(ret)); 236 <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; 237 } 238 239 std::shared_ptr<ArrayBufferAllocator> allocator = 240 ArrayBufferAllocator::<span class="hljs-built_in">Create</span>(); 241 242 Isolate* isolate = <span class="hljs-built_in">NewIsolate</span>(allocator, &loop, platform); 243 <span class="hljs-keyword">if</span> (isolate == <span class="hljs-literal">nullptr</span>) { 244 <span class="hljs-built_in">fprintf</span>(stderr, <span class="hljs-string">"%s: Failed to initialize V8 Isolate\n"</span>, args[<span class="hljs-number">0</span>].<span class="hljs-built_in">c_str</span>()); 245 <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; 246 } 247 248 { 249 <span class="hljs-function">Locker <span class="hljs-title">locker</span><span class="hljs-params">(isolate)</span></span>; 250 <span class="hljs-function">Isolate::Scope <span class="hljs-title">isolate_scope</span><span class="hljs-params">(isolate)</span></span>; 251 252 <span class="hljs-comment">// Create a node::IsolateData instance that will later be released using</span> 253 <span class="hljs-comment">// node::FreeIsolateData().</span> 254 <span class="hljs-function">std::unique_ptr<IsolateData, <span class="hljs-title">decltype</span><span class="hljs-params">(&node::FreeIsolateData)</span>> <span class="hljs-title">isolate_data</span><span class="hljs-params">( 255 node::CreateIsolateData(isolate, &loop, platform, allocator.get()), 256 node::FreeIsolateData)</span></span>; 257 258 <span class="hljs-comment">// Set up a new v8::Context.</span> 259 <span class="hljs-function">HandleScope <span class="hljs-title">handle_scope</span><span class="hljs-params">(isolate)</span></span>; 260 Local<Context> context = node::<span class="hljs-built_in">NewContext</span>(isolate); 261 <span class="hljs-keyword">if</span> (context.<span class="hljs-built_in">IsEmpty</span>()) { 262 <span class="hljs-built_in">fprintf</span>(stderr, <span class="hljs-string">"%s: Failed to initialize V8 Context\n"</span>, args[<span class="hljs-number">0</span>].<span class="hljs-built_in">c_str</span>()); 263 <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; 264 } 265 266 <span class="hljs-comment">// The v8::Context needs to be entered when node::CreateEnvironment() and</span> 267 <span class="hljs-comment">// node::LoadEnvironment() are being called.</span> 268 <span class="hljs-function">Context::Scope <span class="hljs-title">context_scope</span><span class="hljs-params">(context)</span></span>; 269 270 <span class="hljs-comment">// Create a node::Environment instance that will later be released using</span> 271 <span class="hljs-comment">// node::FreeEnvironment().</span> 272 <span class="hljs-function">std::unique_ptr<Environment, <span class="hljs-title">decltype</span><span class="hljs-params">(&node::FreeEnvironment)</span>> <span class="hljs-title">env</span><span class="hljs-params">( 273 node::CreateEnvironment(isolate_data.get(), context, args, exec_args), 274 node::FreeEnvironment)</span></span>; 275 276 <span class="hljs-comment">// Set up the Node.js instance for execution, and run code inside of it.</span> 277 <span class="hljs-comment">// There is also a variant that takes a callback and provides it with</span> 278 <span class="hljs-comment">// the `require` and `process` objects, so that it can manually compile</span> 279 <span class="hljs-comment">// and run scripts as needed.</span> 280 <span class="hljs-comment">// The `require` function inside this script does *not* access the file</span> 281 <span class="hljs-comment">// system, and can only load built-in Node.js modules.</span> 282 <span class="hljs-comment">// `module.createRequire()` is being used to create one that is able to</span> 283 <span class="hljs-comment">// load files from the disk, and uses the standard CommonJS file loader</span> 284 <span class="hljs-comment">// instead of the internal-only `require` function.</span> 285 MaybeLocal<Value> loadenv_ret = node::<span class="hljs-built_in">LoadEnvironment</span>( 286 env.<span class="hljs-built_in">get</span>(), 287 <span class="hljs-string">"const publicRequire ="</span> 288 <span class="hljs-string">" require('module').createRequire(process.cwd() + '/');"</span> 289 <span class="hljs-string">"globalThis.require = publicRequire;"</span> 290 <span class="hljs-string">"require('vm').runInThisContext(process.argv[1]);"</span>); 291 292 <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> 293 <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; 294 295 { 296 <span class="hljs-comment">// SealHandleScope protects against handle leaks from callbacks.</span> 297 <span class="hljs-function">SealHandleScope <span class="hljs-title">seal</span><span class="hljs-params">(isolate)</span></span>; 298 <span class="hljs-type">bool</span> more; 299 <span class="hljs-keyword">do</span> { 300 <span class="hljs-built_in">uv_run</span>(&loop, UV_RUN_DEFAULT); 301 302 <span class="hljs-comment">// V8 tasks on background threads may end up scheduling new tasks in the</span> 303 <span class="hljs-comment">// foreground, which in turn can keep the event loop going. For example,</span> 304 <span class="hljs-comment">// WebAssembly.compile() may do so.</span> 305 platform-><span class="hljs-built_in">DrainTasks</span>(isolate); 306 307 <span class="hljs-comment">// If there are new tasks, continue.</span> 308 more = <span class="hljs-built_in">uv_loop_alive</span>(&loop); 309 <span class="hljs-keyword">if</span> (more) <span class="hljs-keyword">continue</span>; 310 311 <span class="hljs-comment">// node::EmitProcessBeforeExit() is used to emit the 'beforeExit' event</span> 312 <span class="hljs-comment">// on the `process` object.</span> 313 <span class="hljs-keyword">if</span> (node::<span class="hljs-built_in">EmitProcessBeforeExit</span>(env.<span class="hljs-built_in">get</span>()).<span class="hljs-built_in">IsNothing</span>()) 314 <span class="hljs-keyword">break</span>; 315 316 <span class="hljs-comment">// 'beforeExit' can also schedule new work that keeps the event loop</span> 317 <span class="hljs-comment">// running.</span> 318 more = <span class="hljs-built_in">uv_loop_alive</span>(&loop); 319 } <span class="hljs-keyword">while</span> (more == <span class="hljs-literal">true</span>); 320 } 321 322 <span class="hljs-comment">// node::EmitProcessExit() returns the current exit code.</span> 323 exit_code = node::<span class="hljs-built_in">EmitProcessExit</span>(env.<span class="hljs-built_in">get</span>()).<span class="hljs-built_in">FromMaybe</span>(<span class="hljs-number">1</span>); 324 325 <span class="hljs-comment">// node::Stop() can be used to explicitly stop the event loop and keep</span> 326 <span class="hljs-comment">// further JavaScript from running. It can be called from any thread,</span> 327 <span class="hljs-comment">// and will act like worker.terminate() if called from another thread.</span> 328 node::<span class="hljs-built_in">Stop</span>(env.<span class="hljs-built_in">get</span>()); 329 } 330 331 <span class="hljs-comment">// Unregister the Isolate with the platform and add a listener that is called</span> 332 <span class="hljs-comment">// when the Platform is done cleaning up any state it had associated with</span> 333 <span class="hljs-comment">// the Isolate.</span> 334 <span class="hljs-type">bool</span> platform_finished = <span class="hljs-literal">false</span>; 335 platform-><span class="hljs-built_in">AddIsolateFinishedCallback</span>(isolate, [](<span class="hljs-type">void</span>* data) { 336 *<span class="hljs-built_in">static_cast</span><<span class="hljs-type">bool</span>*>(data) = <span class="hljs-literal">true</span>; 337 }, &platform_finished); 338 platform-><span class="hljs-built_in">UnregisterIsolate</span>(isolate); 339 isolate-><span class="hljs-built_in">Dispose</span>(); 340 341 <span class="hljs-comment">// Wait until the platform has cleaned up all relevant resources.</span> 342 <span class="hljs-keyword">while</span> (!platform_finished) 343 <span class="hljs-built_in">uv_run</span>(&loop, UV_RUN_ONCE); 344 <span class="hljs-type">int</span> err = <span class="hljs-built_in">uv_loop_close</span>(&loop); 345 <span class="hljs-built_in">assert</span>(err == <span class="hljs-number">0</span>); 346 347 <span class="hljs-keyword">return</span> exit_code; 348}</code></pre></section> 349 <!-- API END --> 350 </div> 351 </div> 352 </div> 353 <script> 354 'use strict'; 355 { 356 const kCustomPreference = 'customDarkTheme'; 357 const userSettings = sessionStorage.getItem(kCustomPreference); 358 const themeToggleButton = document.getElementById('theme-toggle-btn'); 359 if (userSettings === null && window.matchMedia) { 360 const mq = window.matchMedia('(prefers-color-scheme: dark)'); 361 if ('onchange' in mq) { 362 function mqChangeListener(e) { 363 document.body.classList.toggle('dark-mode', e.matches); 364 } 365 mq.addEventListener('change', mqChangeListener); 366 if (themeToggleButton) { 367 themeToggleButton.addEventListener('click', function() { 368 mq.removeEventListener('change', mqChangeListener); 369 }, { once: true }); 370 } 371 } 372 if (mq.matches) { 373 document.body.classList.add('dark-mode'); 374 } 375 } else if (userSettings === 'true') { 376 document.body.classList.add('dark-mode'); 377 } 378 if (themeToggleButton) { 379 themeToggleButton.hidden = false; 380 themeToggleButton.addEventListener('click', function() { 381 sessionStorage.setItem( 382 kCustomPreference, 383 document.body.classList.toggle('dark-mode') 384 ); 385 }); 386 } 387 } 388 </script> 389</body> 390</html> 391