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Table of contents
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<li><span class="stability_2"><a href="#inspector">Inspector</a></span>
<ul>
<li><span class="stability_1"><a href="#promises-api">Promises API</a></span>
<ul>
<li><a href="#class-inspectorsession">Class: <code>inspector.Session</code></a>
<ul>
<li><a href="#new-inspectorsession"><code>new inspector.Session()</code></a></li>
<li><a href="#event-inspectornotification">Event: <code>'inspectorNotification'</code></a></li>
<li><a href="#event-inspector-protocol-method">Event: <code><inspector-protocol-method></code>;</a></li>
<li><a href="#sessionconnect"><code>session.connect()</code></a></li>
<li><a href="#sessionconnecttomainthread"><code>session.connectToMainThread()</code></a></li>
<li><a href="#sessiondisconnect"><code>session.disconnect()</code></a></li>
<li><a href="#sessionpostmethod-params"><code>session.post(method[, params])</code></a></li>
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<li><a href="#new-inspectorsession_1"><code>new inspector.Session()</code></a></li>
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<li><a href="#event-inspector-protocol-method_1">Event: <code><inspector-protocol-method></code>;</a></li>
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<li><a href="#sessiondisconnect_1"><code>session.disconnect()</code></a></li>
<li><a href="#sessionpostmethod-params-callback"><code>session.post(method[, params][, callback])</code></a></li>
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<a href="#alt-docs" aria-controls="alt-docs">
<span class="picker-arrow"></span>
Other versions
</a>
<div class="picker" tabindex="-1"><ol id="alt-docs"><li><a href="https://nodejs.org/docs/latest-v23.x/api/inspector.html">23.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v22.x/api/inspector.html">22.x <b>LTS</b></a></li>
<li><a href="https://nodejs.org/docs/latest-v21.x/api/inspector.html">21.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v20.x/api/inspector.html">20.x <b>LTS</b></a></li>
<li><a href="https://nodejs.org/docs/latest-v19.x/api/inspector.html">19.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v18.x/api/inspector.html">18.x <b>LTS</b></a></li>
<li><a href="https://nodejs.org/docs/latest-v17.x/api/inspector.html">17.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v16.x/api/inspector.html">16.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v15.x/api/inspector.html">15.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v14.x/api/inspector.html">14.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v13.x/api/inspector.html">13.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v12.x/api/inspector.html">12.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v11.x/api/inspector.html">11.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v10.x/api/inspector.html">10.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v9.x/api/inspector.html">9.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v8.x/api/inspector.html">8.x</a></li></ol></div>
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<li class="picker-header">
<a href="#options-picker" aria-controls="options-picker">
<span class="picker-arrow"></span>
Options
</a>
<div class="picker" tabindex="-1">
<ul id="options-picker">
<li>
<a href="all.html">View on single page</a>
</li>
<li>
<a href="inspector.json">View as JSON</a>
</li>
<li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/inspector.md">Edit on GitHub</a></li>
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<hr>
</header>
<details role="navigation" id="toc" open><summary>Table of contents</summary><ul>
<li><span class="stability_2"><a href="#inspector">Inspector</a></span>
<ul>
<li><span class="stability_1"><a href="#promises-api">Promises API</a></span>
<ul>
<li><a href="#class-inspectorsession">Class: <code>inspector.Session</code></a>
<ul>
<li><a href="#new-inspectorsession"><code>new inspector.Session()</code></a></li>
<li><a href="#event-inspectornotification">Event: <code>'inspectorNotification'</code></a></li>
<li><a href="#event-inspector-protocol-method">Event: <code><inspector-protocol-method></code>;</a></li>
<li><a href="#sessionconnect"><code>session.connect()</code></a></li>
<li><a href="#sessionconnecttomainthread"><code>session.connectToMainThread()</code></a></li>
<li><a href="#sessiondisconnect"><code>session.disconnect()</code></a></li>
<li><a href="#sessionpostmethod-params"><code>session.post(method[, params])</code></a></li>
<li><a href="#example-usage">Example usage</a>
<ul>
<li><a href="#cpu-profiler">CPU profiler</a></li>
<li><a href="#heap-profiler">Heap profiler</a></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
<li><a href="#callback-api">Callback API</a>
<ul>
<li><a href="#class-inspectorsession_1">Class: <code>inspector.Session</code></a>
<ul>
<li><a href="#new-inspectorsession_1"><code>new inspector.Session()</code></a></li>
<li><a href="#event-inspectornotification_1">Event: <code>'inspectorNotification'</code></a></li>
<li><a href="#event-inspector-protocol-method_1">Event: <code><inspector-protocol-method></code>;</a></li>
<li><a href="#sessionconnect_1"><code>session.connect()</code></a></li>
<li><a href="#sessionconnecttomainthread_1"><code>session.connectToMainThread()</code></a></li>
<li><a href="#sessiondisconnect_1"><code>session.disconnect()</code></a></li>
<li><a href="#sessionpostmethod-params-callback"><code>session.post(method[, params][, callback])</code></a></li>
<li><a href="#example-usage_1">Example usage</a>
<ul>
<li><a href="#cpu-profiler_1">CPU profiler</a></li>
<li><a href="#heap-profiler_1">Heap profiler</a></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
<li><a href="#common-objects">Common Objects</a>
<ul>
<li><a href="#inspectorclose"><code>inspector.close()</code></a></li>
<li><a href="#inspectorconsole"><code>inspector.console</code></a></li>
<li><a href="#inspectoropenport-host-wait"><code>inspector.open([port[, host[, wait]]])</code></a></li>
<li><a href="#inspectorurl"><code>inspector.url()</code></a></li>
<li><a href="#inspectorwaitfordebugger"><code>inspector.waitForDebugger()</code></a></li>
</ul>
</li>
<li><a href="#integration-with-devtools">Integration with DevTools</a>
<ul>
<li><span class="stability_1"><a href="#inspectornetworkrequestwillbesentparams"><code>inspector.Network.requestWillBeSent([params])</code></a></span></li>
<li><span class="stability_1"><a href="#inspectornetworkresponsereceivedparams"><code>inspector.Network.responseReceived([params])</code></a></span></li>
<li><span class="stability_1"><a href="#inspectornetworkloadingfinishedparams"><code>inspector.Network.loadingFinished([params])</code></a></span></li>
<li><span class="stability_1"><a href="#inspectornetworkloadingfailedparams"><code>inspector.Network.loadingFailed([params])</code></a></span></li>
</ul>
</li>
<li><a href="#support-of-breakpoints">Support of breakpoints</a></li>
</ul>
</li>
</ul></details>
<div role="main" id="apicontent">
<h2>Inspector<span><a class="mark" href="#inspector" id="inspector">#</a></span><a aria-hidden="true" class="legacy" id="inspector_inspector"></a></h2>
<p></p><div class="api_stability api_stability_2"><a href="documentation.html#stability-index">Stability: 2</a> - Stable</div><p></p>
<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v22.14.0/lib/inspector.js">lib/inspector.js</a></p>
<p>The <code>node:inspector</code> module provides an API for interacting with the V8
inspector.</p>
<p>It can be accessed using:</p>
<pre class="with-53-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> * <span class="hljs-keyword">as</span> inspector <span class="hljs-keyword">from</span> <span class="hljs-string">'node:inspector/promises'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> inspector = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:inspector/promises'</span>);</code><button class="copy-button">copy</button></pre>
<p>or</p>
<pre class="with-44-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> * <span class="hljs-keyword">as</span> inspector <span class="hljs-keyword">from</span> <span class="hljs-string">'node:inspector'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> inspector = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:inspector'</span>);</code><button class="copy-button">copy</button></pre>
<section><h3>Promises API<span><a class="mark" href="#promises-api" id="promises-api">#</a></span><a aria-hidden="true" class="legacy" id="inspector_promises_api"></a></h3>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<div class="api_metadata">
<span>Added in: v19.0.0</span>
</div>
<h4>Class: <code>inspector.Session</code><span><a class="mark" href="#class-inspectorsession" id="class-inspectorsession">#</a></span><a aria-hidden="true" class="legacy" id="inspector_class_inspector_session"></a></h4>
<ul>
<li>Extends: <a href="events.html#class-eventemitter" class="type"><EventEmitter></a></li>
</ul>
<p>The <code>inspector.Session</code> is used for dispatching messages to the V8 inspector
back-end and receiving message responses and notifications.</p>
<h5><code>new inspector.Session()</code><span><a class="mark" href="#new-inspectorsession" id="new-inspectorsession">#</a></span><a aria-hidden="true" class="legacy" id="inspector_new_inspector_session"></a></h5>
<div class="api_metadata">
<span>Added in: v8.0.0</span>
</div>
<p>Create a new instance of the <code>inspector.Session</code> class. The inspector session
needs to be connected through <a href="#sessionconnect"><code>session.connect()</code></a> before the messages
can be dispatched to the inspector backend.</p>
<p>When using <code>Session</code>, the object outputted by the console API will not be
released, unless we performed manually <code>Runtime.DiscardConsoleEntries</code>
command.</p>
<h5>Event: <code>'inspectorNotification'</code><span><a class="mark" href="#event-inspectornotification" id="event-inspectornotification">#</a></span><a aria-hidden="true" class="legacy" id="inspector_event_inspectornotification"></a></h5>
<div class="api_metadata">
<span>Added in: v8.0.0</span>
</div>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The notification message object</li>
</ul>
<p>Emitted when any notification from the V8 Inspector is received.</p>
<pre><code class="language-js">session.<span class="hljs-title function_">on</span>(<span class="hljs-string">'inspectorNotification'</span>, <span class="hljs-function">(<span class="hljs-params">message</span>) =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(message.<span class="hljs-property">method</span>));
<span class="hljs-comment">// Debugger.paused</span>
<span class="hljs-comment">// Debugger.resumed</span></code> <button class="copy-button">copy</button></pre>
<blockquote>
<p><strong>Caveat</strong> Breakpoints with same-thread session is not recommended, see
<a href="#support-of-breakpoints">support of breakpoints</a>.</p>
</blockquote>
<p>It is also possible to subscribe only to notifications with specific method:</p>
<h5>Event: <code><inspector-protocol-method></code>;<span><a class="mark" href="#event-inspector-protocol-method" id="event-inspector-protocol-method">#</a></span><a aria-hidden="true" class="legacy" id="inspector_event_inspector_protocol_method"></a></h5>
<div class="api_metadata">
<span>Added in: v8.0.0</span>
</div>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The notification message object</li>
</ul>
<p>Emitted when an inspector notification is received that has its method field set
to the <code><inspector-protocol-method></code> value.</p>
<p>The following snippet installs a listener on the <a href="https://chromedevtools.github.io/devtools-protocol/v8/Debugger#event-paused"><code>'Debugger.paused'</code></a>
event, and prints the reason for program suspension whenever program
execution is suspended (through breakpoints, for example):</p>
<pre><code class="language-js">session.<span class="hljs-title function_">on</span>(<span class="hljs-string">'Debugger.paused'</span>, <span class="hljs-function">(<span class="hljs-params">{ params }</span>) =></span> {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(params.<span class="hljs-property">hitBreakpoints</span>);
});
<span class="hljs-comment">// [ '/the/file/that/has/the/breakpoint.js:11:0' ]</span></code> <button class="copy-button">copy</button></pre>
<blockquote>
<p><strong>Caveat</strong> Breakpoints with same-thread session is not recommended, see
<a href="#support-of-breakpoints">support of breakpoints</a>.</p>
</blockquote>
<h5><code>session.connect()</code><span><a class="mark" href="#sessionconnect" id="sessionconnect">#</a></span><a aria-hidden="true" class="legacy" id="inspector_session_connect"></a></h5>
<div class="api_metadata">
<span>Added in: v8.0.0</span>
</div>
<p>Connects a session to the inspector back-end.</p>
<h5><code>session.connectToMainThread()</code><span><a class="mark" href="#sessionconnecttomainthread" id="sessionconnecttomainthread">#</a></span><a aria-hidden="true" class="legacy" id="inspector_session_connecttomainthread"></a></h5>
<div class="api_metadata">
<span>Added in: v12.11.0</span>
</div>
<p>Connects a session to the main thread inspector back-end. An exception will
be thrown if this API was not called on a Worker thread.</p>
<h5><code>session.disconnect()</code><span><a class="mark" href="#sessiondisconnect" id="sessiondisconnect">#</a></span><a aria-hidden="true" class="legacy" id="inspector_session_disconnect"></a></h5>
<div class="api_metadata">
<span>Added in: v8.0.0</span>
</div>
<p>Immediately close the session. All pending message callbacks will be called
with an error. <a href="#sessionconnect"><code>session.connect()</code></a> will need to be called to be able to send
messages again. Reconnected session will lose all inspector state, such as
enabled agents or configured breakpoints.</p>
<h5><code>session.post(method[, params])</code><span><a class="mark" href="#sessionpostmethod-params" id="sessionpostmethod-params">#</a></span><a aria-hidden="true" class="legacy" id="inspector_session_post_method_params"></a></h5>
<div class="api_metadata">
<span>Added in: v19.0.0</span>
</div>
<ul>
<li><code>method</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li><code>params</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a></li>
</ul>
<p>Posts a message to the inspector back-end.</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">Session</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:inspector/promises'</span>;
<span class="hljs-keyword">try</span> {
<span class="hljs-keyword">const</span> session = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Session</span>();
session.<span class="hljs-title function_">connect</span>();
<span class="hljs-keyword">const</span> result = <span class="hljs-keyword">await</span> session.<span class="hljs-title function_">post</span>(<span class="hljs-string">'Runtime.evaluate'</span>, { <span class="hljs-attr">expression</span>: <span class="hljs-string">'2 + 2'</span> });
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(result);
} <span class="hljs-keyword">catch</span> (error) {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(error);
}
<span class="hljs-comment">// Output: { result: { type: 'number', value: 4, description: '4' } }</span></code> <button class="copy-button">copy</button></pre>
<p>The latest version of the V8 inspector protocol is published on the
<a href="https://chromedevtools.github.io/devtools-protocol/v8/">Chrome DevTools Protocol Viewer</a>.</p>
<p>Node.js inspector supports all the Chrome DevTools Protocol domains declared
by V8. Chrome DevTools Protocol domain provides an interface for interacting
with one of the runtime agents used to inspect the application state and listen
to the run-time events.</p>
<h5>Example usage<span><a class="mark" href="#example-usage" id="example-usage">#</a></span><a aria-hidden="true" class="legacy" id="inspector_example_usage"></a></h5>
<p>Apart from the debugger, various V8 Profilers are available through the DevTools
protocol.</p>
<h6>CPU profiler<span><a class="mark" href="#cpu-profiler" id="cpu-profiler">#</a></span><a aria-hidden="true" class="legacy" id="inspector_cpu_profiler"></a></h6>
<p>Here's an example showing how to use the <a href="https://chromedevtools.github.io/devtools-protocol/v8/Profiler">CPU Profiler</a>:</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">Session</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:inspector/promises'</span>;
<span class="hljs-keyword">import</span> fs <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs'</span>;
<span class="hljs-keyword">const</span> session = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Session</span>();
session.<span class="hljs-title function_">connect</span>();
<span class="hljs-keyword">await</span> session.<span class="hljs-title function_">post</span>(<span class="hljs-string">'Profiler.enable'</span>);
<span class="hljs-keyword">await</span> session.<span class="hljs-title function_">post</span>(<span class="hljs-string">'Profiler.start'</span>);
<span class="hljs-comment">// Invoke business logic under measurement here...</span>
<span class="hljs-comment">// some time later...</span>
<span class="hljs-keyword">const</span> { profile } = <span class="hljs-keyword">await</span> session.<span class="hljs-title function_">post</span>(<span class="hljs-string">'Profiler.stop'</span>);
<span class="hljs-comment">// Write profile to disk, upload, etc.</span>
fs.<span class="hljs-title function_">writeFileSync</span>(<span class="hljs-string">'./profile.cpuprofile'</span>, <span class="hljs-title class_">JSON</span>.<span class="hljs-title function_">stringify</span>(profile));</code> <button class="copy-button">copy</button></pre>
<h6>Heap profiler<span><a class="mark" href="#heap-profiler" id="heap-profiler">#</a></span><a aria-hidden="true" class="legacy" id="inspector_heap_profiler"></a></h6>
<p>Here's an example showing how to use the <a href="https://chromedevtools.github.io/devtools-protocol/v8/HeapProfiler">Heap Profiler</a>:</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">Session</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:inspector/promises'</span>;
<span class="hljs-keyword">import</span> fs <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs'</span>;
<span class="hljs-keyword">const</span> session = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Session</span>();
<span class="hljs-keyword">const</span> fd = fs.<span class="hljs-title function_">openSync</span>(<span class="hljs-string">'profile.heapsnapshot'</span>, <span class="hljs-string">'w'</span>);
session.<span class="hljs-title function_">connect</span>();
session.<span class="hljs-title function_">on</span>(<span class="hljs-string">'HeapProfiler.addHeapSnapshotChunk'</span>, <span class="hljs-function">(<span class="hljs-params">m</span>) =></span> {
fs.<span class="hljs-title function_">writeSync</span>(fd, m.<span class="hljs-property">params</span>.<span class="hljs-property">chunk</span>);
});
<span class="hljs-keyword">const</span> result = <span class="hljs-keyword">await</span> session.<span class="hljs-title function_">post</span>(<span class="hljs-string">'HeapProfiler.takeHeapSnapshot'</span>, <span class="hljs-literal">null</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'HeapProfiler.takeHeapSnapshot done:'</span>, result);
session.<span class="hljs-title function_">disconnect</span>();
fs.<span class="hljs-title function_">closeSync</span>(fd);</code> <button class="copy-button">copy</button></pre>
</section><section><h3>Callback API<span><a class="mark" href="#callback-api" id="callback-api">#</a></span><a aria-hidden="true" class="legacy" id="inspector_callback_api"></a></h3>
<h4>Class: <code>inspector.Session</code><span><a class="mark" href="#class-inspectorsession_1" id="class-inspectorsession_1">#</a></span><a aria-hidden="true" class="legacy" id="inspector_class_inspector_session_1"></a></h4>
<ul>
<li>Extends: <a href="events.html#class-eventemitter" class="type"><EventEmitter></a></li>
</ul>
<p>The <code>inspector.Session</code> is used for dispatching messages to the V8 inspector
back-end and receiving message responses and notifications.</p>
<h5><code>new inspector.Session()</code><span><a class="mark" href="#new-inspectorsession_1" id="new-inspectorsession_1">#</a></span><a aria-hidden="true" class="legacy" id="inspector_new_inspector_session_1"></a></h5>
<div class="api_metadata">
<span>Added in: v8.0.0</span>
</div>
<p>Create a new instance of the <code>inspector.Session</code> class. The inspector session
needs to be connected through <a href="#sessionconnect"><code>session.connect()</code></a> before the messages
can be dispatched to the inspector backend.</p>
<p>When using <code>Session</code>, the object outputted by the console API will not be
released, unless we performed manually <code>Runtime.DiscardConsoleEntries</code>
command.</p>
<h5>Event: <code>'inspectorNotification'</code><span><a class="mark" href="#event-inspectornotification_1" id="event-inspectornotification_1">#</a></span><a aria-hidden="true" class="legacy" id="inspector_event_inspectornotification_1"></a></h5>
<div class="api_metadata">
<span>Added in: v8.0.0</span>
</div>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The notification message object</li>
</ul>
<p>Emitted when any notification from the V8 Inspector is received.</p>
<pre><code class="language-js">session.<span class="hljs-title function_">on</span>(<span class="hljs-string">'inspectorNotification'</span>, <span class="hljs-function">(<span class="hljs-params">message</span>) =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(message.<span class="hljs-property">method</span>));
<span class="hljs-comment">// Debugger.paused</span>
<span class="hljs-comment">// Debugger.resumed</span></code> <button class="copy-button">copy</button></pre>
<blockquote>
<p><strong>Caveat</strong> Breakpoints with same-thread session is not recommended, see
<a href="#support-of-breakpoints">support of breakpoints</a>.</p>
</blockquote>
<p>It is also possible to subscribe only to notifications with specific method:</p>
<h5>Event: <code><inspector-protocol-method></code>;<span><a class="mark" href="#event-inspector-protocol-method_1" id="event-inspector-protocol-method_1">#</a></span><a aria-hidden="true" class="legacy" id="inspector_event_inspector_protocol_method_1"></a></h5>
<div class="api_metadata">
<span>Added in: v8.0.0</span>
</div>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The notification message object</li>
</ul>
<p>Emitted when an inspector notification is received that has its method field set
to the <code><inspector-protocol-method></code> value.</p>
<p>The following snippet installs a listener on the <a href="https://chromedevtools.github.io/devtools-protocol/v8/Debugger#event-paused"><code>'Debugger.paused'</code></a>
event, and prints the reason for program suspension whenever program
execution is suspended (through breakpoints, for example):</p>
<pre><code class="language-js">session.<span class="hljs-title function_">on</span>(<span class="hljs-string">'Debugger.paused'</span>, <span class="hljs-function">(<span class="hljs-params">{ params }</span>) =></span> {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(params.<span class="hljs-property">hitBreakpoints</span>);
});
<span class="hljs-comment">// [ '/the/file/that/has/the/breakpoint.js:11:0' ]</span></code> <button class="copy-button">copy</button></pre>
<blockquote>
<p><strong>Caveat</strong> Breakpoints with same-thread session is not recommended, see
<a href="#support-of-breakpoints">support of breakpoints</a>.</p>
</blockquote>
<h5><code>session.connect()</code><span><a class="mark" href="#sessionconnect_1" id="sessionconnect_1">#</a></span><a aria-hidden="true" class="legacy" id="inspector_session_connect_1"></a></h5>
<div class="api_metadata">
<span>Added in: v8.0.0</span>
</div>
<p>Connects a session to the inspector back-end.</p>
<h5><code>session.connectToMainThread()</code><span><a class="mark" href="#sessionconnecttomainthread_1" id="sessionconnecttomainthread_1">#</a></span><a aria-hidden="true" class="legacy" id="inspector_session_connecttomainthread_1"></a></h5>
<div class="api_metadata">
<span>Added in: v12.11.0</span>
</div>
<p>Connects a session to the main thread inspector back-end. An exception will
be thrown if this API was not called on a Worker thread.</p>
<h5><code>session.disconnect()</code><span><a class="mark" href="#sessiondisconnect_1" id="sessiondisconnect_1">#</a></span><a aria-hidden="true" class="legacy" id="inspector_session_disconnect_1"></a></h5>
<div class="api_metadata">
<span>Added in: v8.0.0</span>
</div>
<p>Immediately close the session. All pending message callbacks will be called
with an error. <a href="#sessionconnect"><code>session.connect()</code></a> will need to be called to be able to send
messages again. Reconnected session will lose all inspector state, such as
enabled agents or configured breakpoints.</p>
<h5><code>session.post(method[, params][, callback])</code><span><a class="mark" href="#sessionpostmethod-params-callback" id="sessionpostmethod-params-callback">#</a></span><a aria-hidden="true" class="legacy" id="inspector_session_post_method_params_callback"></a></h5>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v18.0.0</td>
<td><p>Passing an invalid callback to the <code>callback</code> argument now throws <code>ERR_INVALID_ARG_TYPE</code> instead of <code>ERR_INVALID_CALLBACK</code>.</p></td></tr>
<tr><td>v8.0.0</td>
<td><p><span>Added in: v8.0.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>method</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li><code>params</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Posts a message to the inspector back-end. <code>callback</code> will be notified when
a response is received. <code>callback</code> is a function that accepts two optional
arguments: error and message-specific result.</p>
<pre><code class="language-js">session.<span class="hljs-title function_">post</span>(<span class="hljs-string">'Runtime.evaluate'</span>, { <span class="hljs-attr">expression</span>: <span class="hljs-string">'2 + 2'</span> },
<span class="hljs-function">(<span class="hljs-params">error, { result }</span>) =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(result));
<span class="hljs-comment">// Output: { type: 'number', value: 4, description: '4' }</span></code> <button class="copy-button">copy</button></pre>
<p>The latest version of the V8 inspector protocol is published on the
<a href="https://chromedevtools.github.io/devtools-protocol/v8/">Chrome DevTools Protocol Viewer</a>.</p>
<p>Node.js inspector supports all the Chrome DevTools Protocol domains declared
by V8. Chrome DevTools Protocol domain provides an interface for interacting
with one of the runtime agents used to inspect the application state and listen
to the run-time events.</p>
<p>You can not set <code>reportProgress</code> to <code>true</code> when sending a
<code>HeapProfiler.takeHeapSnapshot</code> or <code>HeapProfiler.stopTrackingHeapObjects</code>
command to V8.</p>
<h5>Example usage<span><a class="mark" href="#example-usage_1" id="example-usage_1">#</a></span><a aria-hidden="true" class="legacy" id="inspector_example_usage_1"></a></h5>
<p>Apart from the debugger, various V8 Profilers are available through the DevTools
protocol.</p>
<h6>CPU profiler<span><a class="mark" href="#cpu-profiler_1" id="cpu-profiler_1">#</a></span><a aria-hidden="true" class="legacy" id="inspector_cpu_profiler_1"></a></h6>
<p>Here's an example showing how to use the <a href="https://chromedevtools.github.io/devtools-protocol/v8/Profiler">CPU Profiler</a>:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> inspector = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:inspector'</span>);
<span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>);
<span class="hljs-keyword">const</span> session = <span class="hljs-keyword">new</span> inspector.<span class="hljs-title class_">Session</span>();
session.<span class="hljs-title function_">connect</span>();
session.<span class="hljs-title function_">post</span>(<span class="hljs-string">'Profiler.enable'</span>, <span class="hljs-function">() =></span> {
session.<span class="hljs-title function_">post</span>(<span class="hljs-string">'Profiler.start'</span>, <span class="hljs-function">() =></span> {
<span class="hljs-comment">// Invoke business logic under measurement here...</span>
<span class="hljs-comment">// some time later...</span>
session.<span class="hljs-title function_">post</span>(<span class="hljs-string">'Profiler.stop'</span>, <span class="hljs-function">(<span class="hljs-params">err, { profile }</span>) =></span> {
<span class="hljs-comment">// Write profile to disk, upload, etc.</span>
<span class="hljs-keyword">if</span> (!err) {
fs.<span class="hljs-title function_">writeFileSync</span>(<span class="hljs-string">'./profile.cpuprofile'</span>, <span class="hljs-title class_">JSON</span>.<span class="hljs-title function_">stringify</span>(profile));
}
});
});
});</code> <button class="copy-button">copy</button></pre>
<h6>Heap profiler<span><a class="mark" href="#heap-profiler_1" id="heap-profiler_1">#</a></span><a aria-hidden="true" class="legacy" id="inspector_heap_profiler_1"></a></h6>
<p>Here's an example showing how to use the <a href="https://chromedevtools.github.io/devtools-protocol/v8/HeapProfiler">Heap Profiler</a>:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> inspector = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:inspector'</span>);
<span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>);
<span class="hljs-keyword">const</span> session = <span class="hljs-keyword">new</span> inspector.<span class="hljs-title class_">Session</span>();
<span class="hljs-keyword">const</span> fd = fs.<span class="hljs-title function_">openSync</span>(<span class="hljs-string">'profile.heapsnapshot'</span>, <span class="hljs-string">'w'</span>);
session.<span class="hljs-title function_">connect</span>();
session.<span class="hljs-title function_">on</span>(<span class="hljs-string">'HeapProfiler.addHeapSnapshotChunk'</span>, <span class="hljs-function">(<span class="hljs-params">m</span>) =></span> {
fs.<span class="hljs-title function_">writeSync</span>(fd, m.<span class="hljs-property">params</span>.<span class="hljs-property">chunk</span>);
});
session.<span class="hljs-title function_">post</span>(<span class="hljs-string">'HeapProfiler.takeHeapSnapshot'</span>, <span class="hljs-literal">null</span>, <span class="hljs-function">(<span class="hljs-params">err, r</span>) =></span> {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'HeapProfiler.takeHeapSnapshot done:'</span>, err, r);
session.<span class="hljs-title function_">disconnect</span>();
fs.<span class="hljs-title function_">closeSync</span>(fd);
});</code> <button class="copy-button">copy</button></pre>
</section><section><h3>Common Objects<span><a class="mark" href="#common-objects" id="common-objects">#</a></span><a aria-hidden="true" class="legacy" id="inspector_common_objects"></a></h3>
<h4><code>inspector.close()</code><span><a class="mark" href="#inspectorclose" id="inspectorclose">#</a></span><a aria-hidden="true" class="legacy" id="inspector_inspector_close"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v18.10.0</td>
<td><p>The API is exposed in the worker threads.</p></td></tr>
<tr><td>v9.0.0</td>
<td><p><span>Added in: v9.0.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>Attempts to close all remaining connections, blocking the event loop until all
are closed. Once all connections are closed, deactivates the inspector.</p>
<h4><code>inspector.console</code><span><a class="mark" href="#inspectorconsole" id="inspectorconsole">#</a></span><a aria-hidden="true" class="legacy" id="inspector_inspector_console"></a></h4>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> An object to send messages to the remote inspector console.</li>
</ul>
<pre><code class="language-js"><span class="hljs-built_in">require</span>(<span class="hljs-string">'node:inspector'</span>).<span class="hljs-property">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'a message'</span>);</code> <button class="copy-button">copy</button></pre>
<p>The inspector console does not have API parity with Node.js
console.</p>
<h4><code>inspector.open([port[, host[, wait]]])</code><span><a class="mark" href="#inspectoropenport-host-wait" id="inspectoropenport-host-wait">#</a></span><a aria-hidden="true" class="legacy" id="inspector_inspector_open_port_host_wait"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.6.0</td>
<td><p>inspector.open() now returns a <code>Disposable</code> object.</p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>port</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Port to listen on for inspector connections. Optional.
<strong>Default:</strong> what was specified on the CLI.</li>
<li><code>host</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Host to listen on for inspector connections. Optional.
<strong>Default:</strong> what was specified on the CLI.</li>
<li><code>wait</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Block until a client has connected. Optional.
<strong>Default:</strong> <code>false</code>.</li>
<li>Returns: <a href="https://tc39.es/proposal-explicit-resource-management/#sec-disposable-interface" class="type"><Disposable></a> A Disposable that calls <a href="#inspectorclose"><code>inspector.close()</code></a>.</li>
</ul>
<p>Activate inspector on host and port. Equivalent to
<code>node --inspect=[[host:]port]</code>, but can be done programmatically after node has
started.</p>
<p>If wait is <code>true</code>, will block until a client has connected to the inspect port
and flow control has been passed to the debugger client.</p>
<p>See the <a href="cli.html#warning-binding-inspector-to-a-public-ipport-combination-is-insecure">security warning</a> regarding the <code>host</code>
parameter usage.</p>
<h4><code>inspector.url()</code><span><a class="mark" href="#inspectorurl" id="inspectorurl">#</a></span><a aria-hidden="true" class="legacy" id="inspector_inspector_url"></a></h4>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a></li>
</ul>
<p>Return the URL of the active inspector, or <code>undefined</code> if there is none.</p>
<pre><code class="language-console"><span class="hljs-meta prompt_">$ </span><span class="language-bash">node --inspect -p <span class="hljs-string">'inspector.url()'</span></span>
Debugger listening on ws://127.0.0.1:9229/166e272e-7a30-4d09-97ce-f1c012b43c34
For help, see: https://nodejs.org/en/docs/inspector
ws://127.0.0.1:9229/166e272e-7a30-4d09-97ce-f1c012b43c34
<span class="hljs-meta prompt_">
$ </span><span class="language-bash">node --inspect=localhost:3000 -p <span class="hljs-string">'inspector.url()'</span></span>
Debugger listening on ws://localhost:3000/51cf8d0e-3c36-4c59-8efd-54519839e56a
For help, see: https://nodejs.org/en/docs/inspector
ws://localhost:3000/51cf8d0e-3c36-4c59-8efd-54519839e56a
<span class="hljs-meta prompt_">
$ </span><span class="language-bash">node -p <span class="hljs-string">'inspector.url()'</span></span>
undefined</code> <button class="copy-button">copy</button></pre>
<h4><code>inspector.waitForDebugger()</code><span><a class="mark" href="#inspectorwaitfordebugger" id="inspectorwaitfordebugger">#</a></span><a aria-hidden="true" class="legacy" id="inspector_inspector_waitfordebugger"></a></h4>
<div class="api_metadata">
<span>Added in: v12.7.0</span>
</div>
<p>Blocks until a client (existing or connected later) has sent
<code>Runtime.runIfWaitingForDebugger</code> command.</p>
<p>An exception will be thrown if there is no active inspector.</p>
</section><section><h3>Integration with DevTools<span><a class="mark" href="#integration-with-devtools" id="integration-with-devtools">#</a></span><a aria-hidden="true" class="legacy" id="inspector_integration_with_devtools"></a></h3>
<p>The <code>node:inspector</code> module provides an API for integrating with devtools that support Chrome DevTools Protocol.
DevTools frontends connected to a running Node.js instance can capture protocol events emitted from the instance
and display them accordingly to facilitate debugging.
The following methods broadcast a protocol event to all connected frontends.
The <code>params</code> passed to the methods can be optional, depending on the protocol.</p>
<pre><code class="language-js"><span class="hljs-comment">// The `Network.requestWillBeSent` event will be fired.</span>
inspector.<span class="hljs-property">Network</span>.<span class="hljs-title function_">requestWillBeSent</span>({
<span class="hljs-attr">requestId</span>: <span class="hljs-string">'request-id-1'</span>,
<span class="hljs-attr">timestamp</span>: <span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>() / <span class="hljs-number">1000</span>,
<span class="hljs-attr">wallTime</span>: <span class="hljs-title class_">Date</span>.<span class="hljs-title function_">now</span>(),
<span class="hljs-attr">request</span>: {
<span class="hljs-attr">url</span>: <span class="hljs-string">'https://nodejs.org/en'</span>,
<span class="hljs-attr">method</span>: <span class="hljs-string">'GET'</span>,
},
});</code> <button class="copy-button">copy</button></pre>
<h4><code>inspector.Network.requestWillBeSent([params])</code><span><a class="mark" href="#inspectornetworkrequestwillbesentparams" id="inspectornetworkrequestwillbesentparams">#</a></span><a aria-hidden="true" class="legacy" id="inspector_inspector_network_requestwillbesent_params"></a></h4>
<div class="api_metadata">
<span>Added in: v22.6.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<ul>
<li><code>params</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>This feature is only available with the <code>--experimental-network-inspection</code> flag enabled.</p>
<p>Broadcasts the <code>Network.requestWillBeSent</code> event to connected frontends. This event indicates that
the application is about to send an HTTP request.</p>
<h4><code>inspector.Network.responseReceived([params])</code><span><a class="mark" href="#inspectornetworkresponsereceivedparams" id="inspectornetworkresponsereceivedparams">#</a></span><a aria-hidden="true" class="legacy" id="inspector_inspector_network_responsereceived_params"></a></h4>
<div class="api_metadata">
<span>Added in: v22.6.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<ul>
<li><code>params</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>This feature is only available with the <code>--experimental-network-inspection</code> flag enabled.</p>
<p>Broadcasts the <code>Network.responseReceived</code> event to connected frontends. This event indicates that
HTTP response is available.</p>
<h4><code>inspector.Network.loadingFinished([params])</code><span><a class="mark" href="#inspectornetworkloadingfinishedparams" id="inspectornetworkloadingfinishedparams">#</a></span><a aria-hidden="true" class="legacy" id="inspector_inspector_network_loadingfinished_params"></a></h4>
<div class="api_metadata">
<span>Added in: v22.6.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<ul>
<li><code>params</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>This feature is only available with the <code>--experimental-network-inspection</code> flag enabled.</p>
<p>Broadcasts the <code>Network.loadingFinished</code> event to connected frontends. This event indicates that
HTTP request has finished loading.</p>
<h4><code>inspector.Network.loadingFailed([params])</code><span><a class="mark" href="#inspectornetworkloadingfailedparams" id="inspectornetworkloadingfailedparams">#</a></span><a aria-hidden="true" class="legacy" id="inspector_inspector_network_loadingfailed_params"></a></h4>
<div class="api_metadata">
<span>Added in: v22.7.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<ul>
<li><code>params</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>This feature is only available with the <code>--experimental-network-inspection</code> flag enabled.</p>
<p>Broadcasts the <code>Network.loadingFailed</code> event to connected frontends. This event indicates that
HTTP request has failed to load.</p>
</section><section><h3>Support of breakpoints<span><a class="mark" href="#support-of-breakpoints" id="support-of-breakpoints">#</a></span><a aria-hidden="true" class="legacy" id="inspector_support_of_breakpoints"></a></h3>
<p>The Chrome DevTools Protocol <a href="https://chromedevtools.github.io/devtools-protocol/v8/Debugger"><code>Debugger</code> domain</a> allows an
<code>inspector.Session</code> to attach to a program and set breakpoints to step through
the codes.</p>
<p>However, setting breakpoints with a same-thread <code>inspector.Session</code>, which is
connected by <a href="#sessionconnect"><code>session.connect()</code></a>, should be avoided as the program being
attached and paused is exactly the debugger itself. Instead, try connect to the
main thread by <a href="#sessionconnecttomainthread"><code>session.connectToMainThread()</code></a> and set breakpoints in a
worker thread, or connect with a <a href="debugger.html">Debugger</a> program over WebSocket
connection.</p></section>
<!-- API END -->
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