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      <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>
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      <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>
<!--introduced_in=v12.19.0-->

<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 &lt;code&gt;</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">int main(int argc, char** argv) {
  argv = uv_setup_args(argc, argv);
  std::vector&lt;std::string&gt; args(argv, argv + argc);
  // Parse Node.js CLI options, and print any errors that have occurred while
  // trying to parse them.
  std::unique_ptr&lt;node::InitializationResult&gt; result =
      node::InitializeOncePerProcess(args, {
        node::ProcessInitializationFlags::kNoInitializeV8,
        node::ProcessInitializationFlags::kNoInitializeNodeV8Platform
      });

  for (const std::string&amp; error : result-&gt;errors())
    fprintf(stderr, &quot;%s: %s\n&quot;, args[0].c_str(), error.c_str());
  if (result-&gt;early_return() != 0) {
    return result-&gt;exit_code();
  }

  // Create a v8::Platform instance. `MultiIsolatePlatform::Create()` is a way
  // to create a v8::Platform instance that Node.js can use when creating
  // Worker threads. When no `MultiIsolatePlatform` instance is present,
  // Worker threads are disabled.
  std::unique_ptr&lt;MultiIsolatePlatform&gt; platform =
      MultiIsolatePlatform::Create(4);
  V8::InitializePlatform(platform.get());
  V8::Initialize();

  // See below for the contents of this function.
  int ret = RunNodeInstance(
      platform.get(), result-&gt;args(), result-&gt;exec_args());

  V8::Dispose();
  V8::DisposePlatform();

  node::TearDownOncePerProcess();
  return 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>
<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>
</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">int RunNodeInstance(MultiIsolatePlatform* platform,
                    const std::vector&lt;std::string&gt;&amp; args,
                    const std::vector&lt;std::string&gt;&amp; exec_args) {
  int exit_code = 0;

  // Setup up a libuv event loop, v8::Isolate, and Node.js Environment.
  std::vector&lt;std::string&gt; errors;
  std::unique_ptr&lt;CommonEnvironmentSetup&gt; setup =
      CommonEnvironmentSetup::Create(platform, &amp;errors, args, exec_args);
  if (!setup) {
    for (const std::string&amp; err : errors)
      fprintf(stderr, &quot;%s: %s\n&quot;, args[0].c_str(), err.c_str());
    return 1;
  }

  Isolate* isolate = setup-&gt;isolate();
  Environment* env = setup-&gt;env();

  {
    Locker locker(isolate);
    Isolate::Scope isolate_scope(isolate);
    HandleScope handle_scope(isolate);
    // The v8::Context needs to be entered when node::CreateEnvironment() and
    // node::LoadEnvironment() are being called.
    Context::Scope context_scope(setup-&gt;context());

    // Set up the Node.js instance for execution, and run code inside of it.
    // There is also a variant that takes a callback and provides it with
    // the `require` and `process` objects, so that it can manually compile
    // and run scripts as needed.
    // The `require` function inside this script does *not* access the file
    // system, and can only load built-in Node.js modules.
    // `module.createRequire()` is being used to create one that is able to
    // load files from the disk, and uses the standard CommonJS file loader
    // instead of the internal-only `require` function.
    MaybeLocal&lt;Value&gt; loadenv_ret = node::LoadEnvironment(
        env,
        &quot;const publicRequire =&quot;
        &quot;  require(&#39;node:module&#39;).createRequire(process.cwd() + &#39;/&#39;);&quot;
        &quot;globalThis.require = publicRequire;&quot;
        &quot;require(&#39;node:vm&#39;).runInThisContext(process.argv[1]);&quot;);

    if (loadenv_ret.IsEmpty())  // There has been a JS exception.
      return 1;

    exit_code = node::SpinEventLoop(env).FromMaybe(1);

    // node::Stop() can be used to explicitly stop the event loop and keep
    // further JavaScript from running. It can be called from any thread,
    // and will act like worker.terminate() if called from another thread.
    node::Stop(env);
  }

  return exit_code;
}
</code></pre>
</section>
        <!-- API END -->
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Zerion Mini Shell 1.0