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data-id="embedding" class="interior"> 90 <header> 91 <div class="header-container"> 92 <h1>Node.js v14.19.1 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-v14.x/api/embedding.html">14.x <b>LTS</b></a></li></ol> 123 </li> 124 125 <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/embedding.md">Edit on GitHub</a></li> 126 </ul> 127 </div> 128 <hr> 129 </header> 130 131 <details id="toc" open><summary>Table of contents</summary><ul> 132<li><a href="#embedding_c_embedder_api">C++ embedder API</a> 133<ul> 134<li><a href="#embedding_example_embedding_application">Example embedding application</a> 135<ul> 136<li><a href="#embedding_setting_up_per_process_state">Setting up per-process state</a></li> 137<li><a href="#embedding_per_instance_state">Per-instance state</a></li> 138</ul> 139</li> 140</ul> 141</li> 142</ul></details> 143 144 <div id="apicontent"> 145 <h2>C++ embedder API<span><a class="mark" href="#embedding_c_embedder_api" id="embedding_c_embedder_api">#</a></span></h2> 146 147<p>Node.js provides a number of C++ APIs that can be used to execute JavaScript 148in a Node.js environment from other C++ software.</p> 149<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 150source tree. In addition to the APIs exposed by Node.js, some required concepts 151are provided by the V8 embedder API.</p> 152<p>Because using Node.js as an embedded library is different from writing code 153that is executed by Node.js, breaking changes do not follow typical Node.js 154<a href="deprecations.html">deprecation policy</a> and may occur on each semver-major release without prior 155warning.</p> 156<section><h3>Example embedding application<span><a class="mark" href="#embedding_example_embedding_application" id="embedding_example_embedding_application">#</a></span></h3> 157<p>The following sections will provide an overview over how to use these APIs 158to create an application from scratch that will perform the equivalent of 159<code>node -e <code></code>, i.e. that will take a piece of JavaScript and run it in 160a Node.js-specific environment.</p> 161<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> 162<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> 163<p>Node.js requires some per-process state management in order to run:</p> 164<ul> 165<li>Arguments parsing for Node.js <a href="cli.html">CLI options</a>,</li> 166<li>V8 per-process requirements, such as a <code>v8::Platform</code> instance.</li> 167</ul> 168<p>The following example shows how these can be set up. Some class names are from 169the <code>node</code> and <code>v8</code> C++ namespaces, respectively.</p> 170<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>{ 171 argv = <span class="hljs-built_in">uv_setup_args</span>(argc, argv); 172 <span class="hljs-function">std::vector<std::string> <span class="hljs-title">args</span><span class="hljs-params">(argv, argv + argc)</span></span>; 173 std::vector<std::string> exec_args; 174 std::vector<std::string> errors; 175 <span class="hljs-comment">// Parse Node.js CLI options, and print any errors that have occurred while</span> 176 <span class="hljs-comment">// trying to parse them.</span> 177 <span class="hljs-type">int</span> exit_code = node::<span class="hljs-built_in">InitializeNodeWithArgs</span>(&args, &exec_args, &errors); 178 <span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> std::string& error : errors) 179 <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>()); 180 <span class="hljs-keyword">if</span> (exit_code != <span class="hljs-number">0</span>) { 181 <span class="hljs-keyword">return</span> exit_code; 182 } 183 184 <span class="hljs-comment">// Create a v8::Platform instance. `MultiIsolatePlatform::Create()` is a way</span> 185 <span class="hljs-comment">// to create a v8::Platform instance that Node.js can use when creating</span> 186 <span class="hljs-comment">// Worker threads. When no `MultiIsolatePlatform` instance is present,</span> 187 <span class="hljs-comment">// Worker threads are disabled.</span> 188 std::unique_ptr<MultiIsolatePlatform> platform = 189 MultiIsolatePlatform::<span class="hljs-built_in">Create</span>(<span class="hljs-number">4</span>); 190 V8::<span class="hljs-built_in">InitializePlatform</span>(platform.<span class="hljs-built_in">get</span>()); 191 V8::<span class="hljs-built_in">Initialize</span>(); 192 193 <span class="hljs-comment">// See below for the contents of this function.</span> 194 <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); 195 196 V8::<span class="hljs-built_in">Dispose</span>(); 197 V8::<span class="hljs-built_in">ShutdownPlatform</span>(); 198 <span class="hljs-keyword">return</span> ret; 199}</code></pre> 200<h4>Per-instance state<span><a class="mark" href="#embedding_per_instance_state" id="embedding_per_instance_state">#</a></span></h4> 201<p>Node.js has a concept of a “Node.js instance”, that is commonly being referred 202to as <code>node::Environment</code>. Each <code>node::Environment</code> is associated with:</p> 203<ul> 204<li>Exactly one <code>v8::Isolate</code>, i.e. one JS Engine instance,</li> 205<li>Exactly one <code>uv_loop_t</code>, i.e. one event loop, and</li> 206<li>A number of <code>v8::Context</code>s, but exactly one main <code>v8::Context</code>.</li> 207<li>One <code>node::IsolateData</code> instance that contains information that could be 208shared by multiple <code>node::Environment</code>s that use the same <code>v8::Isolate</code>. 209Currently, no testing if performed for this scenario.</li> 210</ul> 211<p>In order to set up a <code>v8::Isolate</code>, an <code>v8::ArrayBuffer::Allocator</code> needs 212to be provided. One possible choice is the default Node.js allocator, which 213can be created through <code>node::ArrayBufferAllocator::Create()</code>. Using the Node.js 214allocator allows minor performance optimizations when addons use the Node.js 215C++ <code>Buffer</code> API, and is required in order to track <code>ArrayBuffer</code> memory in 216<a href="process.html#process_process_memoryusage"><code>process.memoryUsage()</code></a>.</p> 217<p>Additionally, each <code>v8::Isolate</code> that is used for a Node.js instance needs to 218be registered and unregistered with the <code>MultiIsolatePlatform</code> instance, if one 219is being used, in order for the platform to know which event loop to use 220for tasks scheduled by the <code>v8::Isolate</code>.</p> 221<p>The <code>node::NewIsolate()</code> helper function creates a <code>v8::Isolate</code>, 222sets it up with some Node.js-specific hooks (e.g. the Node.js error handler), 223and registers it with the platform automatically.</p> 224<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, 225 <span class="hljs-keyword">const</span> std::vector<std::string>& args, 226 <span class="hljs-keyword">const</span> std::vector<std::string>& exec_args)</span> </span>{ 227 <span class="hljs-type">int</span> exit_code = <span class="hljs-number">0</span>; 228 <span class="hljs-comment">// Set up a libuv event loop.</span> 229 <span class="hljs-type">uv_loop_t</span> loop; 230 <span class="hljs-type">int</span> ret = <span class="hljs-built_in">uv_loop_init</span>(&loop); 231 <span class="hljs-keyword">if</span> (ret != <span class="hljs-number">0</span>) { 232 <span class="hljs-built_in">fprintf</span>(stderr, <span class="hljs-string">"%s: Failed to initialize loop: %s\n"</span>, 233 args[<span class="hljs-number">0</span>].<span class="hljs-built_in">c_str</span>(), 234 <span class="hljs-built_in">uv_err_name</span>(ret)); 235 <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; 236 } 237 238 std::shared_ptr<ArrayBufferAllocator> allocator = 239 ArrayBufferAllocator::<span class="hljs-built_in">Create</span>(); 240 241 Isolate* isolate = <span class="hljs-built_in">NewIsolate</span>(allocator, &loop, platform); 242 <span class="hljs-keyword">if</span> (isolate == <span class="hljs-literal">nullptr</span>) { 243 <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>()); 244 <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; 245 } 246 247 { 248 <span class="hljs-function">Locker <span class="hljs-title">locker</span><span class="hljs-params">(isolate)</span></span>; 249 <span class="hljs-function">Isolate::Scope <span class="hljs-title">isolate_scope</span><span class="hljs-params">(isolate)</span></span>; 250 251 <span class="hljs-comment">// Create a node::IsolateData instance that will later be released using</span> 252 <span class="hljs-comment">// node::FreeIsolateData().</span> 253 <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">( 254 node::CreateIsolateData(isolate, &loop, platform, allocator.get()), 255 node::FreeIsolateData)</span></span>; 256 257 <span class="hljs-comment">// Set up a new v8::Context.</span> 258 <span class="hljs-function">HandleScope <span class="hljs-title">handle_scope</span><span class="hljs-params">(isolate)</span></span>; 259 Local<Context> context = node::<span class="hljs-built_in">NewContext</span>(isolate); 260 <span class="hljs-keyword">if</span> (context.<span class="hljs-built_in">IsEmpty</span>()) { 261 <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>()); 262 <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; 263 } 264 265 <span class="hljs-comment">// The v8::Context needs to be entered when node::CreateEnvironment() and</span> 266 <span class="hljs-comment">// node::LoadEnvironment() are being called.</span> 267 <span class="hljs-function">Context::Scope <span class="hljs-title">context_scope</span><span class="hljs-params">(context)</span></span>; 268 269 <span class="hljs-comment">// Create a node::Environment instance that will later be released using</span> 270 <span class="hljs-comment">// node::FreeEnvironment().</span> 271 <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">( 272 node::CreateEnvironment(isolate_data.get(), context, args, exec_args), 273 node::FreeEnvironment)</span></span>; 274 275 <span class="hljs-comment">// Set up the Node.js instance for execution, and run code inside of it.</span> 276 <span class="hljs-comment">// There is also a variant that takes a callback and provides it with</span> 277 <span class="hljs-comment">// the `require` and `process` objects, so that it can manually compile</span> 278 <span class="hljs-comment">// and run scripts as needed.</span> 279 <span class="hljs-comment">// The `require` function inside this script does *not* access the file</span> 280 <span class="hljs-comment">// system, and can only load built-in Node.js modules.</span> 281 <span class="hljs-comment">// `module.createRequire()` is being used to create one that is able to</span> 282 <span class="hljs-comment">// load files from the disk, and uses the standard CommonJS file loader</span> 283 <span class="hljs-comment">// instead of the internal-only `require` function.</span> 284 MaybeLocal<Value> loadenv_ret = node::<span class="hljs-built_in">LoadEnvironment</span>( 285 env.<span class="hljs-built_in">get</span>(), 286 <span class="hljs-string">"const publicRequire ="</span> 287 <span class="hljs-string">" require('module').createRequire(process.cwd() + '/');"</span> 288 <span class="hljs-string">"globalThis.require = publicRequire;"</span> 289 <span class="hljs-string">"require('vm').runInThisContext(process.argv[1]);"</span>); 290 291 <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> 292 <span class="hljs-keyword">return</span> <span class="hljs-number">1</span>; 293 294 { 295 <span class="hljs-comment">// SealHandleScope protects against handle leaks from callbacks.</span> 296 <span class="hljs-function">SealHandleScope <span class="hljs-title">seal</span><span class="hljs-params">(isolate)</span></span>; 297 <span class="hljs-type">bool</span> more; 298 <span class="hljs-keyword">do</span> { 299 <span class="hljs-built_in">uv_run</span>(&loop, UV_RUN_DEFAULT); 300 301 <span class="hljs-comment">// V8 tasks on background threads may end up scheduling new tasks in the</span> 302 <span class="hljs-comment">// foreground, which in turn can keep the event loop going. For example,</span> 303 <span class="hljs-comment">// WebAssembly.compile() may do so.</span> 304 platform-><span class="hljs-built_in">DrainTasks</span>(isolate); 305 306 <span class="hljs-comment">// If there are new tasks, continue.</span> 307 more = <span class="hljs-built_in">uv_loop_alive</span>(&loop); 308 <span class="hljs-keyword">if</span> (more) <span class="hljs-keyword">continue</span>; 309 310 <span class="hljs-comment">// node::EmitProcessBeforeExit() is used to emit the 'beforeExit' event</span> 311 <span class="hljs-comment">// on the `process` object.</span> 312 <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>()) 313 <span class="hljs-keyword">break</span>; 314 315 <span class="hljs-comment">// 'beforeExit' can also schedule new work that keeps the event loop</span> 316 <span class="hljs-comment">// running.</span> 317 more = <span class="hljs-built_in">uv_loop_alive</span>(&loop); 318 } <span class="hljs-keyword">while</span> (more == <span class="hljs-literal">true</span>); 319 } 320 321 <span class="hljs-comment">// node::EmitProcessExit() returns the current exit code.</span> 322 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>); 323 324 <span class="hljs-comment">// node::Stop() can be used to explicitly stop the event loop and keep</span> 325 <span class="hljs-comment">// further JavaScript from running. It can be called from any thread,</span> 326 <span class="hljs-comment">// and will act like worker.terminate() if called from another thread.</span> 327 node::<span class="hljs-built_in">Stop</span>(env.<span class="hljs-built_in">get</span>()); 328 } 329 330 <span class="hljs-comment">// Unregister the Isolate with the platform and add a listener that is called</span> 331 <span class="hljs-comment">// when the Platform is done cleaning up any state it had associated with</span> 332 <span class="hljs-comment">// the Isolate.</span> 333 <span class="hljs-type">bool</span> platform_finished = <span class="hljs-literal">false</span>; 334 platform-><span class="hljs-built_in">AddIsolateFinishedCallback</span>(isolate, [](<span class="hljs-type">void</span>* data) { 335 *<span class="hljs-built_in">static_cast</span><<span class="hljs-type">bool</span>*>(data) = <span class="hljs-literal">true</span>; 336 }, &platform_finished); 337 platform-><span class="hljs-built_in">UnregisterIsolate</span>(isolate); 338 isolate-><span class="hljs-built_in">Dispose</span>(); 339 340 <span class="hljs-comment">// Wait until the platform has cleaned up all relevant resources.</span> 341 <span class="hljs-keyword">while</span> (!platform_finished) 342 <span class="hljs-built_in">uv_run</span>(&loop, UV_RUN_ONCE); 343 <span class="hljs-type">int</span> err = <span class="hljs-built_in">uv_loop_close</span>(&loop); 344 <span class="hljs-built_in">assert</span>(err == <span class="hljs-number">0</span>); 345 346 <span class="hljs-keyword">return</span> exit_code; 347}</code></pre></section> 348 <!-- API END --> 349 </div> 350 </div> 351 </div> 352 <script> 353 'use strict'; 354 { 355 const kCustomPreference = 'customDarkTheme'; 356 const userSettings = sessionStorage.getItem(kCustomPreference); 357 const themeToggleButton = document.getElementById('theme-toggle-btn'); 358 if (userSettings === null && window.matchMedia) { 359 const mq = window.matchMedia('(prefers-color-scheme: dark)'); 360 if ('onchange' in mq) { 361 function mqChangeListener(e) { 362 document.body.classList.toggle('dark-mode', e.matches); 363 } 364 mq.addEventListener('change', mqChangeListener); 365 if (themeToggleButton) { 366 themeToggleButton.addEventListener('click', function() { 367 mq.removeEventListener('change', mqChangeListener); 368 }, { once: true }); 369 } 370 } 371 if (mq.matches) { 372 document.body.classList.add('dark-mode'); 373 } 374 } else if (userSettings === 'true') { 375 document.body.classList.add('dark-mode'); 376 } 377 if (themeToggleButton) { 378 themeToggleButton.hidden = false; 379 themeToggleButton.addEventListener('click', function() { 380 sessionStorage.setItem( 381 kCustomPreference, 382 document.body.classList.toggle('dark-mode') 383 ); 384 }); 385 } 386 } 387 </script> 388</body> 389</html> 390