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${this.title}
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Code Editor : diagnostics_channel.html
<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width"> <meta name="nodejs.org:node-version" content="v18.17.0"> <title>Diagnostics Channel | Node.js v18.17.0 Documentation</title> <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Lato:400,700,400italic&display=fallback"> <link rel="stylesheet" href="assets/style.css"> <link rel="stylesheet" href="assets/hljs.css"> <link rel="canonical" href="https://nodejs.org/api/diagnostics_channel.html"> <script async defer src="assets/api.js" type="text/javascript"></script> <style>@media(max-width:734px){.with-64-chars>.js-flavor-selector{float:none;margin:0 0 1em auto;}}</style> </head> <body class="alt apidoc" id="api-section-diagnostics_channel"> <div id="content" class="clearfix"> <div id="column2" class="interior"> <div id="intro" class="interior"> <a href="/" title="Go back to the home page"> Node.js </a> </div> <ul> <li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> <li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> </ul> <hr class="line"> <ul> <li><a href="assert.html" class="nav-assert">Assertion testing</a></li> <li><a href="async_context.html" class="nav-async_context">Asynchronous context tracking</a></li> <li><a href="async_hooks.html" class="nav-async_hooks">Async hooks</a></li> <li><a href="buffer.html" class="nav-buffer">Buffer</a></li> <li><a href="addons.html" class="nav-addons">C++ addons</a></li> <li><a href="n-api.html" class="nav-n-api">C/C++ addons with Node-API</a></li> <li><a href="embedding.html" class="nav-embedding">C++ embedder API</a></li> <li><a href="child_process.html" class="nav-child_process">Child processes</a></li> <li><a href="cluster.html" class="nav-cluster">Cluster</a></li> <li><a href="cli.html" class="nav-cli">Command-line options</a></li> <li><a href="console.html" class="nav-console">Console</a></li> <li><a href="corepack.html" class="nav-corepack">Corepack</a></li> <li><a href="crypto.html" class="nav-crypto">Crypto</a></li> <li><a href="debugger.html" class="nav-debugger">Debugger</a></li> <li><a href="deprecations.html" class="nav-deprecations">Deprecated APIs</a></li> <li><a href="diagnostics_channel.html" class="nav-diagnostics_channel active">Diagnostics Channel</a></li> <li><a href="dns.html" class="nav-dns">DNS</a></li> <li><a href="domain.html" class="nav-domain">Domain</a></li> <li><a href="errors.html" class="nav-errors">Errors</a></li> <li><a href="events.html" class="nav-events">Events</a></li> <li><a href="fs.html" class="nav-fs">File system</a></li> <li><a href="globals.html" class="nav-globals">Globals</a></li> <li><a href="http.html" class="nav-http">HTTP</a></li> <li><a href="http2.html" class="nav-http2">HTTP/2</a></li> <li><a href="https.html" class="nav-https">HTTPS</a></li> <li><a href="inspector.html" class="nav-inspector">Inspector</a></li> <li><a href="intl.html" class="nav-intl">Internationalization</a></li> <li><a href="modules.html" class="nav-modules">Modules: CommonJS modules</a></li> <li><a href="esm.html" class="nav-esm">Modules: ECMAScript modules</a></li> <li><a href="module.html" class="nav-module">Modules: <code>node:module</code> API</a></li> <li><a href="packages.html" class="nav-packages">Modules: Packages</a></li> <li><a href="net.html" class="nav-net">Net</a></li> <li><a href="os.html" class="nav-os">OS</a></li> <li><a href="path.html" class="nav-path">Path</a></li> <li><a href="perf_hooks.html" class="nav-perf_hooks">Performance hooks</a></li> <li><a href="permissions.html" class="nav-permissions">Permissions</a></li> <li><a href="process.html" class="nav-process">Process</a></li> <li><a href="punycode.html" class="nav-punycode">Punycode</a></li> <li><a href="querystring.html" class="nav-querystring">Query strings</a></li> <li><a href="readline.html" class="nav-readline">Readline</a></li> <li><a href="repl.html" class="nav-repl">REPL</a></li> <li><a href="report.html" class="nav-report">Report</a></li> <li><a href="single-executable-applications.html" class="nav-single-executable-applications">Single executable applications</a></li> <li><a href="stream.html" class="nav-stream">Stream</a></li> <li><a href="string_decoder.html" class="nav-string_decoder">String decoder</a></li> <li><a href="test.html" class="nav-test">Test runner</a></li> <li><a href="timers.html" class="nav-timers">Timers</a></li> <li><a href="tls.html" class="nav-tls">TLS/SSL</a></li> <li><a href="tracing.html" class="nav-tracing">Trace events</a></li> <li><a href="tty.html" class="nav-tty">TTY</a></li> <li><a href="dgram.html" class="nav-dgram">UDP/datagram</a></li> <li><a href="url.html" class="nav-url">URL</a></li> <li><a href="util.html" class="nav-util">Utilities</a></li> <li><a href="v8.html" class="nav-v8">V8</a></li> <li><a href="vm.html" class="nav-vm">VM</a></li> <li><a href="wasi.html" class="nav-wasi">WASI</a></li> <li><a href="webcrypto.html" class="nav-webcrypto">Web Crypto API</a></li> <li><a href="webstreams.html" class="nav-webstreams">Web Streams API</a></li> <li><a href="worker_threads.html" class="nav-worker_threads">Worker threads</a></li> <li><a href="zlib.html" class="nav-zlib">Zlib</a></li> </ul> <hr class="line"> <ul> <li><a href="https://github.com/nodejs/node" class="nav-https-github-com-nodejs-node">Code repository and issue tracker</a></li> </ul> </div> <div id="column1" data-id="diagnostics_channel" class="interior"> <header class="header"> <div class="header-container"> <h1>Node.js v18.17.0 documentation</h1> <button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" aria-label="Toggle dark mode/light mode" hidden> <svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24"> <path fill="none" d="M0 0h24v24H0z" /> <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"/> <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"/> </svg> <svg xmlns="http://www.w3.org/2000/svg" class="icon light-icon" height="24" width="24"> <path d="M0 0h24v24H0z" fill="none" /> <path d="M6.76 4.84l-1.8-1.79-1.41 1.41 1.79 1.79 1.42-1.41zM4 10.5H1v2h3v-2zm9-9.95h-2V3.5h2V.55zm7.45 3.91l-1.41-1.41-1.79 1.79 1.41 1.41 1.79-1.79zm-3.21 13.7l1.79 1.8 1.41-1.41-1.8-1.79-1.4 1.4zM20 10.5v2h3v-2h-3zm-8-5c-3.31 0-6 2.69-6 6s2.69 6 6 6 6-2.69 6-6-2.69-6-6-6zm-1 16.95h2V19.5h-2v2.95zm-7.45-3.91l1.41 1.41 1.79-1.8-1.41-1.41-1.79 1.8z"/> </svg> </button> </div> <div id="gtoc"> <ul> <li class="pinned-header">Node.js v18.17.0</li> <li class="picker-header"> <a href="#"> <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> Table of contents </a> <div class="picker"><div class="toc"><ul> <li><span class="stability_2"><a href="#diagnostics-channel">Diagnostics Channel</a></span> <ul> <li><a href="#public-api">Public API</a> <ul> <li><a href="#overview">Overview</a> <ul> <li><a href="#diagnostics_channelhassubscribersname"><code>diagnostics_channel.hasSubscribers(name)</code></a></li> <li><a href="#diagnostics_channelchannelname"><code>diagnostics_channel.channel(name)</code></a></li> <li><a href="#diagnostics_channelsubscribename-onmessage"><code>diagnostics_channel.subscribe(name, onMessage)</code></a></li> <li><a href="#diagnostics_channelunsubscribename-onmessage"><code>diagnostics_channel.unsubscribe(name, onMessage)</code></a></li> </ul> </li> <li><a href="#class-channel">Class: <code>Channel</code></a> <ul> <li><a href="#channelhassubscribers"><code>channel.hasSubscribers</code></a></li> <li><a href="#channelpublishmessage"><code>channel.publish(message)</code></a></li> <li><span class="stability_0"><a href="#channelsubscribeonmessage"><code>channel.subscribe(onMessage)</code></a></span></li> <li><span class="stability_0"><a href="#channelunsubscribeonmessage"><code>channel.unsubscribe(onMessage)</code></a></span></li> </ul> </li> <li><span class="stability_1"><a href="#built-in-channels">Built-in Channels</a></span> <ul> <li><a href="#http">HTTP</a></li> </ul> </li> </ul> </li> </ul> </li> </ul></div></div> </li> <li class="picker-header"> <a href="#"> <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> Index </a> <div class="picker"><ul> <li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> <li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> <li> <a href="index.html">Index</a> </li> </ul> <hr class="line"> <ul> <li><a href="assert.html" class="nav-assert">Assertion testing</a></li> <li><a href="async_context.html" class="nav-async_context">Asynchronous context tracking</a></li> <li><a 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Options </a> <div class="picker"> <ul> <li> <a href="all.html">View on single page</a> </li> <li> <a href="diagnostics_channel.json">View as JSON</a> </li> <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/diagnostics_channel.md">Edit on GitHub</a></li> </ul> </div> </li> </ul> </div> <hr> </header> <details id="toc" open><summary>Table of contents</summary><ul> <li><span class="stability_2"><a href="#diagnostics-channel">Diagnostics Channel</a></span> <ul> <li><a href="#public-api">Public API</a> <ul> <li><a href="#overview">Overview</a> <ul> <li><a href="#diagnostics_channelhassubscribersname"><code>diagnostics_channel.hasSubscribers(name)</code></a></li> <li><a href="#diagnostics_channelchannelname"><code>diagnostics_channel.channel(name)</code></a></li> <li><a href="#diagnostics_channelsubscribename-onmessage"><code>diagnostics_channel.subscribe(name, onMessage)</code></a></li> <li><a href="#diagnostics_channelunsubscribename-onmessage"><code>diagnostics_channel.unsubscribe(name, onMessage)</code></a></li> </ul> </li> <li><a href="#class-channel">Class: <code>Channel</code></a> <ul> <li><a href="#channelhassubscribers"><code>channel.hasSubscribers</code></a></li> <li><a href="#channelpublishmessage"><code>channel.publish(message)</code></a></li> <li><span class="stability_0"><a href="#channelsubscribeonmessage"><code>channel.subscribe(onMessage)</code></a></span></li> <li><span class="stability_0"><a href="#channelunsubscribeonmessage"><code>channel.unsubscribe(onMessage)</code></a></span></li> </ul> </li> <li><span class="stability_1"><a href="#built-in-channels">Built-in Channels</a></span> <ul> <li><a href="#http">HTTP</a></li> </ul> </li> </ul> </li> </ul> </li> </ul></details> <div id="apicontent"> <h2>Diagnostics Channel<span><a class="mark" href="#diagnostics-channel" id="diagnostics-channel">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_diagnostics_channel"></a></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v18.13.0</td> <td><p>diagnostics_channel is now Stable.</p></td></tr> <tr><td>v15.1.0, v14.17.0</td> <td><p><span>Added in: v15.1.0, v14.17.0</span></p></td></tr> </tbody></table> </details> </div> <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/v18.17.0/lib/diagnostics_channel.js">lib/diagnostics_channel.js</a></p> <p>The <code>node:diagnostics_channel</code> module provides an API to create named channels to report arbitrary message data for diagnostics purposes.</p> <p>It can be accessed using:</p> <pre class="with-64-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> diagnostics_channel <span class="hljs-keyword">from</span> <span class="hljs-string">'node:diagnostics_channel'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:diagnostics_channel'</span>);</code><button class="copy-button">copy</button></pre> <p>It is intended that a module writer wanting to report diagnostics messages will create one or many top-level channels to report messages through. Channels may also be acquired at runtime but it is not encouraged due to the additional overhead of doing so. Channels may be exported for convenience, but as long as the name is known it can be acquired anywhere.</p> <p>If you intend for your module to produce diagnostics data for others to consume it is recommended that you include documentation of what named channels are used along with the shape of the message data. Channel names should generally include the module name to avoid collisions with data from other modules.</p> <section><h3>Public API<span><a class="mark" href="#public-api" id="public-api">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_public_api"></a></h3> <h4>Overview<span><a class="mark" href="#overview" id="overview">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_overview"></a></h4> <p>Following is a simple overview of the public API.</p> <pre class="with-64-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> diagnostics_channel <span class="hljs-keyword">from</span> <span class="hljs-string">'node:diagnostics_channel'</span>; <span class="hljs-comment">// Get a reusable channel object</span> <span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); <span class="hljs-keyword">function</span> <span class="hljs-title function_">onMessage</span>(<span class="hljs-params">message, name</span>) { <span class="hljs-comment">// Received data</span> } <span class="hljs-comment">// Subscribe to the channel</span> diagnostics_channel.<span class="hljs-title function_">subscribe</span>(<span class="hljs-string">'my-channel'</span>, onMessage); <span class="hljs-comment">// Check if the channel has an active subscriber</span> <span class="hljs-keyword">if</span> (channel.<span class="hljs-property">hasSubscribers</span>) { <span class="hljs-comment">// Publish data to the channel</span> channel.<span class="hljs-title function_">publish</span>({ <span class="hljs-attr">some</span>: <span class="hljs-string">'data'</span>, }); } <span class="hljs-comment">// Unsubscribe from the channel</span> diagnostics_channel.<span class="hljs-title function_">unsubscribe</span>(<span class="hljs-string">'my-channel'</span>, onMessage);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:diagnostics_channel'</span>); <span class="hljs-comment">// Get a reusable channel object</span> <span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); <span class="hljs-keyword">function</span> <span class="hljs-title function_">onMessage</span>(<span class="hljs-params">message, name</span>) { <span class="hljs-comment">// Received data</span> } <span class="hljs-comment">// Subscribe to the channel</span> diagnostics_channel.<span class="hljs-title function_">subscribe</span>(<span class="hljs-string">'my-channel'</span>, onMessage); <span class="hljs-comment">// Check if the channel has an active subscriber</span> <span class="hljs-keyword">if</span> (channel.<span class="hljs-property">hasSubscribers</span>) { <span class="hljs-comment">// Publish data to the channel</span> channel.<span class="hljs-title function_">publish</span>({ <span class="hljs-attr">some</span>: <span class="hljs-string">'data'</span>, }); } <span class="hljs-comment">// Unsubscribe from the channel</span> diagnostics_channel.<span class="hljs-title function_">unsubscribe</span>(<span class="hljs-string">'my-channel'</span>, onMessage);</code><button class="copy-button">copy</button></pre> <h5><code>diagnostics_channel.hasSubscribers(name)</code><span><a class="mark" href="#diagnostics_channelhassubscribersname" id="diagnostics_channelhassubscribersname">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_diagnostics_channel_hassubscribers_name"></a></h5> <div class="api_metadata"> <span>Added in: v15.1.0, v14.17.0</span> </div> <ul> <li><code>name</code> <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#Symbol_type" class="type"><symbol></a> The channel name</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If there are active subscribers</li> </ul> <p>Check if there are active subscribers to the named channel. This is helpful if the message you want to send might be expensive to prepare.</p> <p>This API is optional but helpful when trying to publish messages from very performance-sensitive code.</p> <pre class="with-64-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> diagnostics_channel <span class="hljs-keyword">from</span> <span class="hljs-string">'node:diagnostics_channel'</span>; <span class="hljs-keyword">if</span> (diagnostics_channel.<span class="hljs-title function_">hasSubscribers</span>(<span class="hljs-string">'my-channel'</span>)) { <span class="hljs-comment">// There are subscribers, prepare and publish message</span> }</code><code class="language-js cjs"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:diagnostics_channel'</span>); <span class="hljs-keyword">if</span> (diagnostics_channel.<span class="hljs-title function_">hasSubscribers</span>(<span class="hljs-string">'my-channel'</span>)) { <span class="hljs-comment">// There are subscribers, prepare and publish message</span> }</code><button class="copy-button">copy</button></pre> <h5><code>diagnostics_channel.channel(name)</code><span><a class="mark" href="#diagnostics_channelchannelname" id="diagnostics_channelchannelname">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_diagnostics_channel_channel_name"></a></h5> <div class="api_metadata"> <span>Added in: v15.1.0, v14.17.0</span> </div> <ul> <li><code>name</code> <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#Symbol_type" class="type"><symbol></a> The channel name</li> <li>Returns: <a href="diagnostics_channel.html#class-channel" class="type"><Channel></a> The named channel object</li> </ul> <p>This is the primary entry-point for anyone wanting to publish to a named channel. It produces a channel object which is optimized to reduce overhead at publish time as much as possible.</p> <pre class="with-64-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> diagnostics_channel <span class="hljs-keyword">from</span> <span class="hljs-string">'node:diagnostics_channel'</span>; <span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:diagnostics_channel'</span>); <span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>);</code><button class="copy-button">copy</button></pre> <h5><code>diagnostics_channel.subscribe(name, onMessage)</code><span><a class="mark" href="#diagnostics_channelsubscribename-onmessage" id="diagnostics_channelsubscribename-onmessage">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_diagnostics_channel_subscribe_name_onmessage"></a></h5> <div class="api_metadata"> <span>Added in: v18.7.0</span> </div> <ul> <li><code>name</code> <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#Symbol_type" class="type"><symbol></a> The channel name</li> <li><code>onMessage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The handler to receive channel messages <ul> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The message data</li> <li><code>name</code> <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#Symbol_type" class="type"><symbol></a> The name of the channel</li> </ul> </li> </ul> <p>Register a message handler to subscribe to this channel. This message handler will be run synchronously whenever a message is published to the channel. Any errors thrown in the message handler will trigger an <a href="process.html#event-uncaughtexception"><code>'uncaughtException'</code></a>.</p> <pre class="with-64-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> diagnostics_channel <span class="hljs-keyword">from</span> <span class="hljs-string">'node:diagnostics_channel'</span>; diagnostics_channel.<span class="hljs-title function_">subscribe</span>(<span class="hljs-string">'my-channel'</span>, <span class="hljs-function">(<span class="hljs-params">message, name</span>) =></span> { <span class="hljs-comment">// Received data</span> });</code><code class="language-js cjs"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:diagnostics_channel'</span>); diagnostics_channel.<span class="hljs-title function_">subscribe</span>(<span class="hljs-string">'my-channel'</span>, <span class="hljs-function">(<span class="hljs-params">message, name</span>) =></span> { <span class="hljs-comment">// Received data</span> });</code><button class="copy-button">copy</button></pre> <h5><code>diagnostics_channel.unsubscribe(name, onMessage)</code><span><a class="mark" href="#diagnostics_channelunsubscribename-onmessage" id="diagnostics_channelunsubscribename-onmessage">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_diagnostics_channel_unsubscribe_name_onmessage"></a></h5> <div class="api_metadata"> <span>Added in: v18.7.0</span> </div> <ul> <li><code>name</code> <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#Symbol_type" class="type"><symbol></a> The channel name</li> <li><code>onMessage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The previous subscribed handler to remove</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> if the handler was found, <code>false</code> otherwise.</li> </ul> <p>Remove a message handler previously registered to this channel with <a href="#diagnostics_channelsubscribename-onmessage"><code>diagnostics_channel.subscribe(name, onMessage)</code></a>.</p> <pre class="with-64-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> diagnostics_channel <span class="hljs-keyword">from</span> <span class="hljs-string">'node:diagnostics_channel'</span>; <span class="hljs-keyword">function</span> <span class="hljs-title function_">onMessage</span>(<span class="hljs-params">message, name</span>) { <span class="hljs-comment">// Received data</span> } diagnostics_channel.<span class="hljs-title function_">subscribe</span>(<span class="hljs-string">'my-channel'</span>, onMessage); diagnostics_channel.<span class="hljs-title function_">unsubscribe</span>(<span class="hljs-string">'my-channel'</span>, onMessage);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:diagnostics_channel'</span>); <span class="hljs-keyword">function</span> <span class="hljs-title function_">onMessage</span>(<span class="hljs-params">message, name</span>) { <span class="hljs-comment">// Received data</span> } diagnostics_channel.<span class="hljs-title function_">subscribe</span>(<span class="hljs-string">'my-channel'</span>, onMessage); diagnostics_channel.<span class="hljs-title function_">unsubscribe</span>(<span class="hljs-string">'my-channel'</span>, onMessage);</code><button class="copy-button">copy</button></pre> <h4>Class: <code>Channel</code><span><a class="mark" href="#class-channel" id="class-channel">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_class_channel"></a></h4> <div class="api_metadata"> <span>Added in: v15.1.0, v14.17.0</span> </div> <p>The class <code>Channel</code> represents an individual named channel within the data pipeline. It is used to track subscribers and to publish messages when there are subscribers present. It exists as a separate object to avoid channel lookups at publish time, enabling very fast publish speeds and allowing for heavy use while incurring very minimal cost. Channels are created with <a href="#diagnostics_channelchannelname"><code>diagnostics_channel.channel(name)</code></a>, constructing a channel directly with <code>new Channel(name)</code> is not supported.</p> <h5><code>channel.hasSubscribers</code><span><a class="mark" href="#channelhassubscribers" id="channelhassubscribers">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_channel_hassubscribers"></a></h5> <div class="api_metadata"> <span>Added in: v15.1.0, v14.17.0</span> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If there are active subscribers</li> </ul> <p>Check if there are active subscribers to this channel. This is helpful if the message you want to send might be expensive to prepare.</p> <p>This API is optional but helpful when trying to publish messages from very performance-sensitive code.</p> <pre class="with-64-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> diagnostics_channel <span class="hljs-keyword">from</span> <span class="hljs-string">'node:diagnostics_channel'</span>; <span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); <span class="hljs-keyword">if</span> (channel.<span class="hljs-property">hasSubscribers</span>) { <span class="hljs-comment">// There are subscribers, prepare and publish message</span> }</code><code class="language-js cjs"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:diagnostics_channel'</span>); <span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); <span class="hljs-keyword">if</span> (channel.<span class="hljs-property">hasSubscribers</span>) { <span class="hljs-comment">// There are subscribers, prepare and publish message</span> }</code><button class="copy-button">copy</button></pre> <h5><code>channel.publish(message)</code><span><a class="mark" href="#channelpublishmessage" id="channelpublishmessage">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_channel_publish_message"></a></h5> <div class="api_metadata"> <span>Added in: v15.1.0, v14.17.0</span> </div> <ul> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The message to send to the channel subscribers</li> </ul> <p>Publish a message to any subscribers to the channel. This will trigger message handlers synchronously so they will execute within the same context.</p> <pre class="with-64-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> diagnostics_channel <span class="hljs-keyword">from</span> <span class="hljs-string">'node:diagnostics_channel'</span>; <span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); channel.<span class="hljs-title function_">publish</span>({ <span class="hljs-attr">some</span>: <span class="hljs-string">'message'</span>, });</code><code class="language-js cjs"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:diagnostics_channel'</span>); <span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); channel.<span class="hljs-title function_">publish</span>({ <span class="hljs-attr">some</span>: <span class="hljs-string">'message'</span>, });</code><button class="copy-button">copy</button></pre> <h5><code>channel.subscribe(onMessage)</code><span><a class="mark" href="#channelsubscribeonmessage" id="channelsubscribeonmessage">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_channel_subscribe_onmessage"></a></h5> <div class="api_metadata"> <span>Added in: v15.1.0, v14.17.0</span><span>Deprecated since: v18.7.0</span> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <a href="#diagnostics_channelsubscribename-onmessage"><code>diagnostics_channel.subscribe(name, onMessage)</code></a></div><p></p> <ul> <li><code>onMessage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The handler to receive channel messages <ul> <li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The message data</li> <li><code>name</code> <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#Symbol_type" class="type"><symbol></a> The name of the channel</li> </ul> </li> </ul> <p>Register a message handler to subscribe to this channel. This message handler will be run synchronously whenever a message is published to the channel. Any errors thrown in the message handler will trigger an <a href="process.html#event-uncaughtexception"><code>'uncaughtException'</code></a>.</p> <pre class="with-64-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> diagnostics_channel <span class="hljs-keyword">from</span> <span class="hljs-string">'node:diagnostics_channel'</span>; <span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); channel.<span class="hljs-title function_">subscribe</span>(<span class="hljs-function">(<span class="hljs-params">message, name</span>) =></span> { <span class="hljs-comment">// Received data</span> });</code><code class="language-js cjs"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:diagnostics_channel'</span>); <span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); channel.<span class="hljs-title function_">subscribe</span>(<span class="hljs-function">(<span class="hljs-params">message, name</span>) =></span> { <span class="hljs-comment">// Received data</span> });</code><button class="copy-button">copy</button></pre> <h5><code>channel.unsubscribe(onMessage)</code><span><a class="mark" href="#channelunsubscribeonmessage" id="channelunsubscribeonmessage">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_channel_unsubscribe_onmessage"></a></h5> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v18.7.0</td> <td><p><span>Deprecated since: v18.7.0</span></p></td></tr> <tr><td>v17.1.0, v16.14.0, v14.19.0</td> <td><p>Added return value. Added to channels without subscribers.</p></td></tr> <tr><td>v15.1.0, v14.17.0</td> <td><p><span>Added in: v15.1.0, v14.17.0</span></p></td></tr> </tbody></table> </details> </div> <p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <a href="#diagnostics_channelunsubscribename-onmessage"><code>diagnostics_channel.unsubscribe(name, onMessage)</code></a></div><p></p> <ul> <li><code>onMessage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The previous subscribed handler to remove</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> if the handler was found, <code>false</code> otherwise.</li> </ul> <p>Remove a message handler previously registered to this channel with <a href="#channelsubscribeonmessage"><code>channel.subscribe(onMessage)</code></a>.</p> <pre class="with-64-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> diagnostics_channel <span class="hljs-keyword">from</span> <span class="hljs-string">'node:diagnostics_channel'</span>; <span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); <span class="hljs-keyword">function</span> <span class="hljs-title function_">onMessage</span>(<span class="hljs-params">message, name</span>) { <span class="hljs-comment">// Received data</span> } channel.<span class="hljs-title function_">subscribe</span>(onMessage); channel.<span class="hljs-title function_">unsubscribe</span>(onMessage);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:diagnostics_channel'</span>); <span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); <span class="hljs-keyword">function</span> <span class="hljs-title function_">onMessage</span>(<span class="hljs-params">message, name</span>) { <span class="hljs-comment">// Received data</span> } channel.<span class="hljs-title function_">subscribe</span>(onMessage); channel.<span class="hljs-title function_">unsubscribe</span>(onMessage);</code><button class="copy-button">copy</button></pre> <h4>Built-in Channels<span><a class="mark" href="#built-in-channels" id="built-in-channels">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_built_in_channels"></a></h4> <p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p> <p>While the diagnostics_channel API is now considered stable, the built-in channels currently available are not. Each channel must be declared stable independently.</p> <h5>HTTP<span><a class="mark" href="#http" id="http">#</a></span><a aria-hidden="true" class="legacy" id="diagnostics_channel_http"></a></h5> <p><code>http.client.request.start</code></p> <ul> <li><code>request</code> <a href="http.html#class-httpclientrequest" class="type"><http.ClientRequest></a></li> </ul> <p>Emitted when client starts a request.</p> <p><code>http.client.response.finish</code></p> <ul> <li><code>request</code> <a href="http.html#class-httpclientrequest" class="type"><http.ClientRequest></a></li> <li><code>response</code> <a href="http.html#class-httpincomingmessage" class="type"><http.IncomingMessage></a></li> </ul> <p>Emitted when client receives a response.</p> <p><code>http.server.request.start</code></p> <ul> <li><code>request</code> <a href="http.html#class-httpincomingmessage" class="type"><http.IncomingMessage></a></li> <li><code>response</code> <a href="http.html#class-httpserverresponse" class="type"><http.ServerResponse></a></li> <li><code>socket</code> <a href="net.html#class-netsocket" class="type"><net.Socket></a></li> <li><code>server</code> <a href="http.html#class-httpserver" class="type"><http.Server></a></li> </ul> <p>Emitted when server receives a request.</p> <p><code>http.server.response.finish</code></p> <ul> <li><code>request</code> <a href="http.html#class-httpincomingmessage" class="type"><http.IncomingMessage></a></li> <li><code>response</code> <a href="http.html#class-httpserverresponse" class="type"><http.ServerResponse></a></li> <li><code>socket</code> <a href="net.html#class-netsocket" class="type"><net.Socket></a></li> <li><code>server</code> <a href="http.html#class-httpserver" class="type"><http.Server></a></li> </ul> <p>Emitted when server sends a response.</p> <p><code>net.client.socket</code></p> <ul> <li><code>socket</code> <a href="net.html#class-netsocket" class="type"><net.Socket></a></li> </ul> <p>Emitted when a new TCP or pipe client socket is created.</p> <p><code>net.server.socket</code></p> <ul> <li><code>socket</code> <a href="net.html#class-netsocket" class="type"><net.Socket></a></li> </ul> <p>Emitted when a new TCP or pipe connection is received.</p> <p><code>udp.socket</code></p> <ul> <li><code>socket</code> <a href="dgram.html#class-dgramsocket" class="type"><dgram.Socket></a></li> </ul> <p>Emitted when a new UDP socket is created.</p></section> <!-- API END --> </div> </div> </div> </body> </html>
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