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data-id="embedding" class="interior"> 90 <header> 91 <div class="header-container"> 92 <h1>Node.js v14.21.2 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-v16.x/api/embedding.html">16.x <b>LTS</b></a></li> 123<li><a href="https://nodejs.org/docs/latest-v15.x/api/embedding.html">15.x</a></li> 124<li><a href="https://nodejs.org/docs/latest-v14.x/api/embedding.html">14.x <b>LTS</b></a></li></ol> 125 </li> 126 127 <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/embedding.md">Edit on GitHub</a></li> 128 </ul> 129 </div> 130 <hr> 131 </header> 132 133 <details id="toc" open><summary>Table of contents</summary><ul> 134<li><a href="#embedding_c_embedder_api">C++ embedder API</a> 135<ul> 136<li><a href="#embedding_example_embedding_application">Example embedding application</a> 137<ul> 138<li><a href="#embedding_setting_up_per_process_state">Setting up per-process state</a></li> 139<li><a href="#embedding_per_instance_state">Per-instance state</a></li> 140</ul> 141</li> 142</ul> 143</li> 144</ul></details> 145 146 <div id="apicontent"> 147 <h2>C++ embedder API<span><a class="mark" href="#embedding_c_embedder_api" id="embedding_c_embedder_api">#</a></span></h2> 148 149<p>Node.js provides a number of C++ APIs that can be used to execute JavaScript 150in a Node.js environment from other C++ software.</p> 151<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 152source tree. In addition to the APIs exposed by Node.js, some required concepts 153are provided by the V8 embedder API.</p> 154<p>Because using Node.js as an embedded library is different from writing code 155that is executed by Node.js, breaking changes do not follow typical Node.js 156<a href="deprecations.html">deprecation policy</a> and may occur on each semver-major release without prior 157warning.</p> 158<section><h3>Example embedding application<span><a class="mark" href="#embedding_example_embedding_application" id="embedding_example_embedding_application">#</a></span></h3> 159<p>The following sections will provide an overview over how to use these APIs 160to create an application from scratch that will perform the equivalent of 161<code>node -e <code></code>, i.e. that will take a piece of JavaScript and run it in 162a Node.js-specific environment.</p> 163<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> 164<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> 165<p>Node.js requires some per-process state management in order to run:</p> 166<ul> 167<li>Arguments parsing for Node.js <a href="cli.html">CLI options</a>,</li> 168<li>V8 per-process requirements, such as a <code>v8::Platform</code> instance.</li> 169</ul> 170<p>The following example shows how these can be set up. Some class names are from 171the <code>node</code> and <code>v8</code> C++ namespaces, respectively.</p> 172<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>{ 173 argv = <span class="hljs-built_in">uv_setup_args</span>(argc, argv); 174 <span class="hljs-function">std::vector<std::string> <span class="hljs-title">args</span><span class="hljs-params">(argv, argv + argc)</span></span>; 175 std::vector<std::string> exec_args; 176 std::vector<std::string> errors; 177 <span class="hljs-comment">// Parse Node.js CLI options, and print any errors that have occurred while</span> 178 <span class="hljs-comment">// trying to parse them.</span> 179 <span class="hljs-type">int</span> exit_code = node::<span class="hljs-built_in">InitializeNodeWithArgs</span>(&args, &exec_args, &errors); 180 <span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> std::string& error : errors) 181 <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>()); 182 <span class="hljs-keyword">if</span> (exit_code != <span class="hljs-number">0</span>) { 183 <span class="hljs-keyword">return</span> exit_code; 184 } 185 186 <span class="hljs-comment">// Create a v8::Platform instance. `MultiIsolatePlatform::Create()` is a way</span> 187 <span class="hljs-comment">// to create a v8::Platform instance that Node.js can use when creating</span> 188 <span class="hljs-comment">// Worker threads. When no `MultiIsolatePlatform` instance is present,</span> 189 <span class="hljs-comment">// Worker threads are disabled.</span> 190 std::unique_ptr<MultiIsolatePlatform> platform = 191 MultiIsolatePlatform::<span class="hljs-built_in">Create</span>(<span class="hljs-number">4</span>); 192 V8::<span class="hljs-built_in">InitializePlatform</span>(platform.<span class="hljs-built_in">get</span>()); 193 V8::<span class="hljs-built_in">Initialize</span>(); 194 195 <span class="hljs-comment">// See below for the contents of this function.</span> 196 <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); 197 198 V8::<span class="hljs-built_in">Dispose</span>(); 199 V8::<span class="hljs-built_in">ShutdownPlatform</span>(); 200 <span class="hljs-keyword">return</span> ret; 201}</code></pre> 202<h4>Per-instance state<span><a class="mark" href="#embedding_per_instance_state" id="embedding_per_instance_state">#</a></span></h4> 203<p>Node.js has a concept of a “Node.js instance”, that is commonly being referred 204to as <code>node::Environment</code>. Each <code>node::Environment</code> is associated with:</p> 205<ul> 206<li>Exactly one <code>v8::Isolate</code>, i.e. one JS Engine instance,</li> 207<li>Exactly one <code>uv_loop_t</code>, i.e. one event loop, and</li> 208<li>A number of <code>v8::Context</code>s, but exactly one main <code>v8::Context</code>.</li> 209<li>One <code>node::IsolateData</code> instance that contains information that could be 210shared by multiple <code>node::Environment</code>s that use the same <code>v8::Isolate</code>. 211Currently, no testing if performed for this scenario.</li> 212</ul> 213<p>In order to set up a <code>v8::Isolate</code>, an <code>v8::ArrayBuffer::Allocator</code> needs 214to be provided. One possible choice is the default Node.js allocator, which 215can be created through <code>node::ArrayBufferAllocator::Create()</code>. Using the Node.js 216allocator allows minor performance optimizations when addons use the Node.js 217C++ <code>Buffer</code> API, and is required in order to track <code>ArrayBuffer</code> memory in 218<a href="process.html#process_process_memoryusage"><code>process.memoryUsage()</code></a>.</p> 219<p>Additionally, each <code>v8::Isolate</code> that is used for a Node.js instance needs to 220be registered and unregistered with the <code>MultiIsolatePlatform</code> instance, if one 221is being used, in order for the platform to know which event loop to use 222for tasks scheduled by the <code>v8::Isolate</code>.</p> 223<p>The <code>node::NewIsolate()</code> helper function creates a <code>v8::Isolate</code>, 224sets it up with some Node.js-specific hooks (e.g. the Node.js error handler), 225and registers it with the platform automatically.</p> 226<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, 227 <span class="hljs-keyword">const</span> std::vector<std::string>& args, 228 <span class="hljs-keyword">const</span> std::vector<std::string>& exec_args)</span> </span>{ 229 <span class="hljs-type">int</span> exit_code = <span class="hljs-number">0</span>; 230 <span class="hljs-comment">// Set up a libuv event loop.</span> 231 <span class="hljs-type">uv_loop_t</span> loop; 232 <span class="hljs-type">int</span> ret = <span class="hljs-built_in">uv_loop_init</span>(&loop); 233 <span class="hljs-keyword">if</span> (ret != <span class="hljs-number">0</span>) { 234 <span class="hljs-built_in">fprintf</span>(stderr, <span class="hljs-string">"%s: Failed to initialize loop: %s\n"</span>, 235 args[<span class="hljs-number">0</span>].<span class="hljs-built_in">c_str</span>(), 236 <span class="hljs-built_in">uv_err_name</span>(ret)); 237 <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; 238 } 239 240 std::shared_ptr<ArrayBufferAllocator> allocator = 241 ArrayBufferAllocator::<span class="hljs-built_in">Create</span>(); 242 243 Isolate* isolate = <span class="hljs-built_in">NewIsolate</span>(allocator, &loop, platform); 244 <span class="hljs-keyword">if</span> (isolate == <span class="hljs-literal">nullptr</span>) { 245 <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>()); 246 <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; 247 } 248 249 { 250 <span class="hljs-function">Locker <span class="hljs-title">locker</span><span class="hljs-params">(isolate)</span></span>; 251 <span class="hljs-function">Isolate::Scope <span class="hljs-title">isolate_scope</span><span class="hljs-params">(isolate)</span></span>; 252 253 <span class="hljs-comment">// Create a node::IsolateData instance that will later be released using</span> 254 <span class="hljs-comment">// node::FreeIsolateData().</span> 255 <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">( 256 node::CreateIsolateData(isolate, &loop, platform, allocator.get()), 257 node::FreeIsolateData)</span></span>; 258 259 <span class="hljs-comment">// Set up a new v8::Context.</span> 260 <span class="hljs-function">HandleScope <span class="hljs-title">handle_scope</span><span class="hljs-params">(isolate)</span></span>; 261 Local<Context> context = node::<span class="hljs-built_in">NewContext</span>(isolate); 262 <span class="hljs-keyword">if</span> (context.<span class="hljs-built_in">IsEmpty</span>()) { 263 <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>()); 264 <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; 265 } 266 267 <span class="hljs-comment">// The v8::Context needs to be entered when node::CreateEnvironment() and</span> 268 <span class="hljs-comment">// node::LoadEnvironment() are being called.</span> 269 <span class="hljs-function">Context::Scope <span class="hljs-title">context_scope</span><span class="hljs-params">(context)</span></span>; 270 271 <span class="hljs-comment">// Create a node::Environment instance that will later be released using</span> 272 <span class="hljs-comment">// node::FreeEnvironment().</span> 273 <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">( 274 node::CreateEnvironment(isolate_data.get(), context, args, exec_args), 275 node::FreeEnvironment)</span></span>; 276 277 <span class="hljs-comment">// Set up the Node.js instance for execution, and run code inside of it.</span> 278 <span class="hljs-comment">// There is also a variant that takes a callback and provides it with</span> 279 <span class="hljs-comment">// the `require` and `process` objects, so that it can manually compile</span> 280 <span class="hljs-comment">// and run scripts as needed.</span> 281 <span class="hljs-comment">// The `require` function inside this script does *not* access the file</span> 282 <span class="hljs-comment">// system, and can only load built-in Node.js modules.</span> 283 <span class="hljs-comment">// `module.createRequire()` is being used to create one that is able to</span> 284 <span class="hljs-comment">// load files from the disk, and uses the standard CommonJS file loader</span> 285 <span class="hljs-comment">// instead of the internal-only `require` function.</span> 286 MaybeLocal<Value> loadenv_ret = node::<span class="hljs-built_in">LoadEnvironment</span>( 287 env.<span class="hljs-built_in">get</span>(), 288 <span class="hljs-string">"const publicRequire ="</span> 289 <span class="hljs-string">" require('module').createRequire(process.cwd() + '/');"</span> 290 <span class="hljs-string">"globalThis.require = publicRequire;"</span> 291 <span class="hljs-string">"require('vm').runInThisContext(process.argv[1]);"</span>); 292 293 <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> 294 <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; 295 296 { 297 <span class="hljs-comment">// SealHandleScope protects against handle leaks from callbacks.</span> 298 <span class="hljs-function">SealHandleScope <span class="hljs-title">seal</span><span class="hljs-params">(isolate)</span></span>; 299 <span class="hljs-type">bool</span> more; 300 <span class="hljs-keyword">do</span> { 301 <span class="hljs-built_in">uv_run</span>(&loop, UV_RUN_DEFAULT); 302 303 <span class="hljs-comment">// V8 tasks on background threads may end up scheduling new tasks in the</span> 304 <span class="hljs-comment">// foreground, which in turn can keep the event loop going. For example,</span> 305 <span class="hljs-comment">// WebAssembly.compile() may do so.</span> 306 platform-><span class="hljs-built_in">DrainTasks</span>(isolate); 307 308 <span class="hljs-comment">// If there are new tasks, continue.</span> 309 more = <span class="hljs-built_in">uv_loop_alive</span>(&loop); 310 <span class="hljs-keyword">if</span> (more) <span class="hljs-keyword">continue</span>; 311 312 <span class="hljs-comment">// node::EmitProcessBeforeExit() is used to emit the 'beforeExit' event</span> 313 <span class="hljs-comment">// on the `process` object.</span> 314 <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>()) 315 <span class="hljs-keyword">break</span>; 316 317 <span class="hljs-comment">// 'beforeExit' can also schedule new work that keeps the event loop</span> 318 <span class="hljs-comment">// running.</span> 319 more = <span class="hljs-built_in">uv_loop_alive</span>(&loop); 320 } <span class="hljs-keyword">while</span> (more == <span class="hljs-literal">true</span>); 321 } 322 323 <span class="hljs-comment">// node::EmitProcessExit() returns the current exit code.</span> 324 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>); 325 326 <span class="hljs-comment">// node::Stop() can be used to explicitly stop the event loop and keep</span> 327 <span class="hljs-comment">// further JavaScript from running. It can be called from any thread,</span> 328 <span class="hljs-comment">// and will act like worker.terminate() if called from another thread.</span> 329 node::<span class="hljs-built_in">Stop</span>(env.<span class="hljs-built_in">get</span>()); 330 } 331 332 <span class="hljs-comment">// Unregister the Isolate with the platform and add a listener that is called</span> 333 <span class="hljs-comment">// when the Platform is done cleaning up any state it had associated with</span> 334 <span class="hljs-comment">// the Isolate.</span> 335 <span class="hljs-type">bool</span> platform_finished = <span class="hljs-literal">false</span>; 336 platform-><span class="hljs-built_in">AddIsolateFinishedCallback</span>(isolate, [](<span class="hljs-type">void</span>* data) { 337 *<span class="hljs-built_in">static_cast</span><<span class="hljs-type">bool</span>*>(data) = <span class="hljs-literal">true</span>; 338 }, &platform_finished); 339 platform-><span class="hljs-built_in">UnregisterIsolate</span>(isolate); 340 isolate-><span class="hljs-built_in">Dispose</span>(); 341 342 <span class="hljs-comment">// Wait until the platform has cleaned up all relevant resources.</span> 343 <span class="hljs-keyword">while</span> (!platform_finished) 344 <span class="hljs-built_in">uv_run</span>(&loop, UV_RUN_ONCE); 345 <span class="hljs-type">int</span> err = <span class="hljs-built_in">uv_loop_close</span>(&loop); 346 <span class="hljs-built_in">assert</span>(err == <span class="hljs-number">0</span>); 347 348 <span class="hljs-keyword">return</span> exit_code; 349}</code></pre></section> 350 <!-- API END --> 351 </div> 352 </div> 353 </div> 354 <script> 355 'use strict'; 356 { 357 const kCustomPreference = 'customDarkTheme'; 358 const userSettings = sessionStorage.getItem(kCustomPreference); 359 const themeToggleButton = document.getElementById('theme-toggle-btn'); 360 if (userSettings === null && window.matchMedia) { 361 const mq = window.matchMedia('(prefers-color-scheme: dark)'); 362 if ('onchange' in mq) { 363 function mqChangeListener(e) { 364 document.body.classList.toggle('dark-mode', e.matches); 365 } 366 mq.addEventListener('change', mqChangeListener); 367 if (themeToggleButton) { 368 themeToggleButton.addEventListener('click', function() { 369 mq.removeEventListener('change', mqChangeListener); 370 }, { once: true }); 371 } 372 } 373 if (mq.matches) { 374 document.body.classList.add('dark-mode'); 375 } 376 } else if (userSettings === 'true') { 377 document.body.classList.add('dark-mode'); 378 } 379 if (themeToggleButton) { 380 themeToggleButton.hidden = false; 381 themeToggleButton.addEventListener('click', function() { 382 sessionStorage.setItem( 383 kCustomPreference, 384 document.body.classList.toggle('dark-mode') 385 ); 386 }); 387 } 388 } 389 </script> 390</body> 391</html> 392