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---
title: Worker.postMessage()
slug: Web/API/Worker/postMessage
translation_of: Web/API/Worker/postMessage
---
<p>{{APIRef("Web Workers API")}}</p>
<p><a href="https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API">Web Workers API</a> posee un metodo llamado <code><strong>postMessage()</strong></code> el cual envia un mensaje al ambito del worker. Este metodo acepta un parametro, el cual es un dato enviado al worker. El dato puede ser un valor o objeto controlado por el algoritmo strctured clone (incluye referencias ciclicas).</p>
<p>El Worker puede enviar de vuelta información al hilo que lo genero usando el metodo {{domxref("DedicatedWorkerGlobalScope.postMessage")}}.</p>
<h2 id="Syntax">Syntax</h2>
<pre class="brush: js">myWorker.postMessage(aMessage, transferList);</pre>
<h3 id="Parameters">Parameters</h3>
<dl>
<dt><em>aMessage</em></dt>
<dd>The object to deliver to the worker; this will be in the data field in the event delivered to the {{domxref("DedicatedWorkerGlobalScope.onmessage")}} handler. This may be any value or JavaScript object handled by the <a href="/en-US/docs/Web/Guide/DOM/The_structured_clone_algorithm" title="http://www.whatwg.org/specs/web-apps/current-work/multipage/common-dom-interfaces.html#transferable">structured clone</a> algorithm, which includes cyclical references.</dd>
<dt><em>transferList</em> {{optional_inline}}</dt>
<dd>An optional <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" title="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array">array</a> of {{domxref("Transferable")}} objects to transfer ownership of. If the ownership of an object is transferred, it becomes unusable (<em>neutered</em>) in the context it was sent from and it becomes available only to the worker it was sent to.</dd>
<dd>Only {{domxref("MessagePort")}} and {{domxref("ArrayBuffer")}} objects can be transferred.</dd>
</dl>
<h3 id="Returns">Returns</h3>
<p>Void.</p>
<h2 id="Example">Example</h2>
<p>The following code snippet shows creation of a {{domxref("Worker")}} object using the {{domxref("Worker.Worker", "Worker()")}} constructor. When either of two form inputs (<code>first</code> and <code>second</code>) have their values changed, {{event("change")}} events invoke <code>postMessage()</code> to send the value of both inputs to the current worker.</p>
<pre class="brush: js">var myWorker = new Worker("worker.js");
first.onchange = function() {
myWorker.postMessage([first.value,second.value]);
console.log('Message posted to worker');
}
second.onchange = function() {
myWorker.postMessage([first.value,second.value]);
console.log('Message posted to worker');
}
</pre>
<p>For a full example, see our<a class="external external-icon" href="https://github.com/mdn/simple-web-worker">Basic dedicated worker example</a> (<a class="external external-icon" dir="ltr" href="mailto:aguilahorus@gmail.com">run dedicated worker</a>).</p>
<div class="note">
<p><strong>Note</strong>: <code>postMessage()</code> can only send a single object at once. As seen above, if you want to pass multiple values you can send an array.</p>
</div>
<h2 id="Transfer_Example">Transfer Example</h2>
<p>This example is of a Firefox addon that transfers an ArrayBuffer from the main thread to the ChromeWorker, and then the ChromeWorker trasnfers it back to the main thread.</p>
<h4 id="Main_thread_code">Main thread code:</h4>
<pre class="brush: js">var myWorker = new ChromeWorker(self.path + 'myWorker.js');
function handleMessageFromWorker(msg) {
console.log('incoming message from worker, msg:', msg);
switch (msg.data.aTopic) {
case 'do_sendMainArrBuff':
sendMainArrBuff(msg.data.aBuf)
break;
default:
throw 'no aTopic on incoming message to ChromeWorker';
}
}
myWorker.addEventListener('message', handleMessageFromWorker);
// Ok lets create the buffer and send it
var arrBuf = new ArrayBuffer(8);
console.info('arrBuf.byteLength pre transfer:', arrBuf.byteLength);
myWorker.postMessage(
{
aTopic: 'do_sendWorkerArrBuff',
aBuf: arrBuf // The array buffer that we passed to the transferrable section 3 lines below
},
[
arrBuf // The array buffer we created 9 lines above
]
);
console.info('arrBuf.byteLength post transfer:', arrBuf.byteLength);
</pre>
<h4 id="Worker_code">Worker code</h4>
<pre class="brush: js">self.onmessage = function (msg) {
switch (msg.data.aTopic) {
case 'do_sendWorkerArrBuff':
sendWorkerArrBuff(msg.data.aBuf)
break;
default:
throw 'no aTopic on incoming message to ChromeWorker';
}
}
function sendWorkerArrBuff(aBuf) {
console.info('from worker, PRE send back aBuf.byteLength:', aBuf.byteLength);
self.postMessage({aTopic:'do_sendMainArrBuff', aBuf:aBuf}, [aBuf]);
console.info('from worker, POST send back aBuf.byteLength:', aBuf.byteLength);
}
</pre>
<h4 id="Output_logged">Output logged</h4>
<pre>arrBuf.byteLength pre transfer: 8 bootstrap.js:40
arrBuf.byteLength post transfer: 0 bootstrap.js:42
from worker, PRE send back aBuf.byteLength: 8 myWorker.js:5:2
incoming message from worker, msg: message { ... } bootstrap.js:20
got back buf in main thread, aBuf.byteLength: 8 bootstrap.js:12
from worker, POST send back aBuf.byteLength: 0 myWorker.js:7:2</pre>
<p>We see that byteLength goes to 0 as it is trasnferred. To see a fully working example of this Firefox demo addon see here: <a href="https://github.com/Noitidart/ChromeWorker/tree/aca57d9cadc4e68af16201bdecbfb6f9a6f9ca6b">GitHub :: ChromeWorker - demo-transfer-arraybuffer</a></p>
<h2 id="Specifications">Specifications</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td>{{SpecName('HTML WHATWG', "#dom-worker-postmessage", "Worker.postMessage()")}}</td>
<td>{{Spec2('HTML WHATWG')}}</td>
<td>No change from {{SpecName("Web Workers")}}.</td>
</tr>
<tr>
<td>{{SpecName('Web Workers', "#dom-worker-postmessage", "Worker.postMessage()")}}</td>
<td>{{Spec2('Web Workers')}}</td>
<td>Initial definition.</td>
</tr>
</tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<div>{{CompatibilityTable}}</div>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Chrome</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari (WebKit)</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>10.0 [1]</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Android</th>
<th>Firefox Mobile (Gecko)</th>
<th>Firefox OS (Gecko)</th>
<th>IE Phone</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>10.0 [1]</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
</tr>
</tbody>
</table>
</div>
<p>[1] Internet Explorer does not support {{domxref("Transferable")}} objects.</p>
<h2 id="See_also">See also</h2>
<ul>
<li>The {{domxref("Worker")}} interface it belongs to.</li>
</ul>
|
