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href="https://nodejs.org/docs/latest-v15.x/api/diagnostics_channel.html">15.x</a></li> 123<li><a href="https://nodejs.org/docs/latest-v14.x/api/diagnostics_channel.html">14.x <b>LTS</b></a></li></ol> 124 </li> 125 126 <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/diagnostics_channel.md">Edit on GitHub</a></li> 127 </ul> 128 </div> 129 <hr> 130 </header> 131 132 <details id="toc" open><summary>Table of contents</summary><ul> 133<li><span class="stability_1"><a href="#diagnostics_channel_diagnostics_channel">Diagnostics Channel</a></span> 134<ul> 135<li><a href="#diagnostics_channel_public_api">Public API</a> 136<ul> 137<li><a href="#diagnostics_channel_overview">Overview</a> 138<ul> 139<li><a href="#diagnostics_channel_diagnostics_channel_hassubscribers_name"><code>diagnostics_channel.hasSubscribers(name)</code></a></li> 140<li><a href="#diagnostics_channel_diagnostics_channel_channel_name"><code>diagnostics_channel.channel(name)</code></a></li> 141</ul> 142</li> 143<li><a href="#diagnostics_channel_class_channel">Class: <code>Channel</code></a> 144<ul> 145<li><a href="#diagnostics_channel_channel_hassubscribers"><code>channel.hasSubscribers</code></a></li> 146<li><a href="#diagnostics_channel_channel_publish_message"><code>channel.publish(message)</code></a></li> 147<li><a href="#diagnostics_channel_channel_subscribe_onmessage"><code>channel.subscribe(onMessage)</code></a></li> 148<li><a href="#diagnostics_channel_channel_unsubscribe_onmessage"><code>channel.unsubscribe(onMessage)</code></a></li> 149</ul> 150</li> 151</ul> 152</li> 153</ul> 154</li> 155</ul></details> 156 157 <div id="apicontent"> 158 <h2>Diagnostics Channel<span><a class="mark" href="#diagnostics_channel_diagnostics_channel" id="diagnostics_channel_diagnostics_channel">#</a></span></h2> 159 160<p></p><div class="api_stability api_stability_1"><a href="documentation.html#documentation_stability_index">Stability: 1</a> - Experimental</div><p></p> 161<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v14.20.1/lib/diagnostics_channel.js">lib/diagnostics_channel.js</a></p> 162<p>The <code>diagnostics_channel</code> module provides an API to create named channels 163to report arbitrary message data for diagnostics purposes.</p> 164<p>It can be accessed using:</p> 165<pre><code class="language-js"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'diagnostics_channel'</span>);</code></pre> 166<p>It is intended that a module writer wanting to report diagnostics messages 167will create one or many top-level channels to report messages through. 168Channels may also be acquired at runtime but it is not encouraged 169due to the additional overhead of doing so. Channels may be exported for 170convenience, but as long as the name is known it can be acquired anywhere.</p> 171<p>If you intend for your module to produce diagnostics data for others to 172consume it is recommended that you include documentation of what named 173channels are used along with the shape of the message data. Channel names 174should generally include the module name to avoid collisions with data from 175other modules.</p> 176<section><h3>Public API<span><a class="mark" href="#diagnostics_channel_public_api" id="diagnostics_channel_public_api">#</a></span></h3> 177<h4>Overview<span><a class="mark" href="#diagnostics_channel_overview" id="diagnostics_channel_overview">#</a></span></h4> 178<p>Following is a simple overview of the public API.</p> 179<pre><code class="language-js"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'diagnostics_channel'</span>); 180 181<span class="hljs-comment">// Get a reusable channel object</span> 182<span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); 183 184<span class="hljs-comment">// Subscribe to the channel</span> 185channel.<span class="hljs-title function_">subscribe</span>(<span class="hljs-function">(<span class="hljs-params">message, name</span>) =></span> { 186 <span class="hljs-comment">// Received data</span> 187}); 188 189<span class="hljs-comment">// Check if the channel has an active subscriber</span> 190<span class="hljs-keyword">if</span> (channel.<span class="hljs-property">hasSubscribers</span>) { 191 <span class="hljs-comment">// Publish data to the channel</span> 192 channel.<span class="hljs-title function_">publish</span>({ 193 <span class="hljs-attr">some</span>: <span class="hljs-string">'data'</span> 194 }); 195}</code></pre> 196<h5><code>diagnostics_channel.hasSubscribers(name)</code><span><a class="mark" href="#diagnostics_channel_diagnostics_channel_hassubscribers_name" id="diagnostics_channel_diagnostics_channel_hassubscribers_name">#</a></span></h5> 197<ul> 198<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> 199<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> 200</ul> 201<p>Check if there are active subscribers to the named channel. This is helpful if 202the message you want to send might be expensive to prepare.</p> 203<p>This API is optional but helpful when trying to publish messages from very 204performance-sensitive code.</p> 205<pre><code class="language-js"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'diagnostics_channel'</span>); 206 207<span class="hljs-keyword">if</span> (diagnostics_channel.<span class="hljs-title function_">hasSubscribers</span>(<span class="hljs-string">'my-channel'</span>)) { 208 <span class="hljs-comment">// There are subscribers, prepare and publish message</span> 209}</code></pre> 210<h5><code>diagnostics_channel.channel(name)</code><span><a class="mark" href="#diagnostics_channel_diagnostics_channel_channel_name" id="diagnostics_channel_diagnostics_channel_channel_name">#</a></span></h5> 211<ul> 212<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> 213<li>Returns: <a href="diagnostics_channel.html#diagnostics_channel_class_channel" class="type"><Channel></a> The named channel object</li> 214</ul> 215<p>This is the primary entry-point for anyone wanting to interact with a named 216channel. It produces a channel object which is optimized to reduce overhead at 217publish time as much as possible.</p> 218<pre><code class="language-js"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'diagnostics_channel'</span>); 219 220<span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>);</code></pre> 221<h4>Class: <code>Channel</code><span><a class="mark" href="#diagnostics_channel_class_channel" id="diagnostics_channel_class_channel">#</a></span></h4> 222<p>The class <code>Channel</code> represents an individual named channel within the data 223pipeline. It is use to track subscribers and to publish messages when there 224are subscribers present. It exists as a separate object to avoid channel 225lookups at publish time, enabling very fast publish speeds and allowing 226for heavy use while incurring very minimal cost. Channels are created with 227<a href="#diagnostics_channel_diagnostics_channel_channel_name"><code>diagnostics_channel.channel(name)</code></a>, constructing a channel directly 228with <code>new Channel(name)</code> is not supported.</p> 229<h5><code>channel.hasSubscribers</code><span><a class="mark" href="#diagnostics_channel_channel_hassubscribers" id="diagnostics_channel_channel_hassubscribers">#</a></span></h5> 230<ul> 231<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> 232</ul> 233<p>Check if there are active subscribers to this channel. This is helpful if 234the message you want to send might be expensive to prepare.</p> 235<p>This API is optional but helpful when trying to publish messages from very 236performance-sensitive code.</p> 237<pre><code class="language-js"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'diagnostics_channel'</span>); 238 239<span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); 240 241<span class="hljs-keyword">if</span> (channel.<span class="hljs-property">hasSubscribers</span>) { 242 <span class="hljs-comment">// There are subscribers, prepare and publish message</span> 243}</code></pre> 244<h5><code>channel.publish(message)</code><span><a class="mark" href="#diagnostics_channel_channel_publish_message" id="diagnostics_channel_channel_publish_message">#</a></span></h5> 245<ul> 246<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> 247</ul> 248<p>Publish a message to any subscribers to the channel. This will trigger 249message handlers synchronously so they will execute within the same context.</p> 250<pre><code class="language-js"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'diagnostics_channel'</span>); 251 252<span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); 253 254channel.<span class="hljs-title function_">publish</span>({ 255 <span class="hljs-attr">some</span>: <span class="hljs-string">'message'</span> 256});</code></pre> 257<h5><code>channel.subscribe(onMessage)</code><span><a class="mark" href="#diagnostics_channel_channel_subscribe_onmessage" id="diagnostics_channel_channel_subscribe_onmessage">#</a></span></h5> 258<ul> 259<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 260<ul> 261<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> 262<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> 263</ul> 264</li> 265</ul> 266<p>Register a message handler to subscribe to this channel. This message handler 267will be run synchronously whenever a message is published to the channel. Any 268errors thrown in the message handler will trigger an <a href="process.html#process_event_uncaughtexception"><code>'uncaughtException'</code></a>.</p> 269<pre><code class="language-js"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'diagnostics_channel'</span>); 270 271<span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); 272 273channel.<span class="hljs-title function_">subscribe</span>(<span class="hljs-function">(<span class="hljs-params">message, name</span>) =></span> { 274 <span class="hljs-comment">// Received data</span> 275});</code></pre> 276<h5><code>channel.unsubscribe(onMessage)</code><span><a class="mark" href="#diagnostics_channel_channel_unsubscribe_onmessage" id="diagnostics_channel_channel_unsubscribe_onmessage">#</a></span></h5> 277<div class="api_metadata"> 278<details class="changelog"><summary>History</summary> 279<table> 280<tbody><tr><th>Version</th><th>Changes</th></tr> 281<tr><td>v14.19.0</td> 282<td><p>Added return value. Added to channels without subscribers.</p></td></tr> 283<tr><td>v14.17.0</td> 284<td><p><span>Added in: v14.17.0</span></p></td></tr> 285</tbody></table> 286</details> 287</div> 288<ul> 289<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> 290<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> 291</ul> 292<p>Remove a message handler previously registered to this channel with 293<a href="#diagnostics_channel_channel_subscribe_onmessage"><code>channel.subscribe(onMessage)</code></a>.</p> 294<pre><code class="language-js"><span class="hljs-keyword">const</span> diagnostics_channel = <span class="hljs-built_in">require</span>(<span class="hljs-string">'diagnostics_channel'</span>); 295 296<span class="hljs-keyword">const</span> channel = diagnostics_channel.<span class="hljs-title function_">channel</span>(<span class="hljs-string">'my-channel'</span>); 297 298<span class="hljs-keyword">function</span> <span class="hljs-title function_">onMessage</span>(<span class="hljs-params">message, name</span>) { 299 <span class="hljs-comment">// Received data</span> 300} 301 302channel.<span class="hljs-title function_">subscribe</span>(onMessage); 303 304channel.<span class="hljs-title function_">unsubscribe</span>(onMessage);</code></pre></section> 305 <!-- API END --> 306 </div> 307 </div> 308 </div> 309 <script> 310 'use strict'; 311 { 312 const kCustomPreference = 'customDarkTheme'; 313 const userSettings = sessionStorage.getItem(kCustomPreference); 314 const themeToggleButton = document.getElementById('theme-toggle-btn'); 315 if (userSettings === null && window.matchMedia) { 316 const mq = window.matchMedia('(prefers-color-scheme: dark)'); 317 if ('onchange' in mq) { 318 function mqChangeListener(e) { 319 document.body.classList.toggle('dark-mode', e.matches); 320 } 321 mq.addEventListener('change', mqChangeListener); 322 if (themeToggleButton) { 323 themeToggleButton.addEventListener('click', function() { 324 mq.removeEventListener('change', mqChangeListener); 325 }, { once: true }); 326 } 327 } 328 if (mq.matches) { 329 document.body.classList.add('dark-mode'); 330 } 331 } else if (userSettings === 'true') { 332 document.body.classList.add('dark-mode'); 333 } 334 if (themeToggleButton) { 335 themeToggleButton.hidden = false; 336 themeToggleButton.addEventListener('click', function() { 337 sessionStorage.setItem( 338 kCustomPreference, 339 document.body.classList.toggle('dark-mode') 340 ); 341 }); 342 } 343 } 344 </script> 345</body> 346</html> 347