---
title: MessageChannel.port2
slug: Web/API/MessageChannel/port2
translation_of: Web/API/MessageChannel/port2
---
<p>{{APIRef("HTML DOM")}}</p>

<p>{{domxref("MessageChannel")}}接口的 <code><strong>port2</strong></code> 是一个只读属性，返回消息通道的第二个端口，该端口连接到通道另一端的上下文，也就是发送消息时的目的地。</p>

<p>{{AvailableInWorkers}}</p>

<h2 id="语法">语法</h2>

<pre class="syntaxbox">channel.port2;</pre>

<h3 id="值">值</h3>

<p>表示通道第二个端口的一个{{domxref("MessagePort")}}对象，该端口附加到通道另一端的上下文。</p>

<p> </p>

<h2 id="示例">示例</h2>

<p>如下代码所示，通过{{domxref("MessageChannel()", "MessageChannel.MessageChannel")}}构造函数创建了一个新的通道。当IFrame加载完毕，我们使用{{domxref("MessagePort.postMessage")}}将一条消息以及port2传递给IFrame。handleMessage处理程序响应从IFrame发回的消息（使用 {{domxref("MessagePort.onmessage")}}），将其放入段落中。{{domxref("MessageChannel.port1")}}已经监听，以检测消息何时到达。</p>

<pre class="brush: js">var channel = new MessageChannel();
var para = document.querySelector('p');

var ifr = document.querySelector('iframe');
var otherWindow = ifr.contentWindow;

ifr.addEventListener("load", iframeLoaded, false);

function iframeLoaded() {
  otherWindow.postMessage('Hello from the main page!', '*', [channel.port2]);
}

channel.port1.onmessage = handleMessage;
function handleMessage(e) {
  para.innerHTML = e.data;
}   </pre>

<p>有关完整的运行示例，请参阅我们在GitHub的 <a class="external external-icon" href="https://github.com/mdn/channel-messaging-basic-demo">channel messaging basic demo</a>  (<a class="external external-icon" href="http://mdn.github.io/channel-messaging-basic-demo/">run it live too</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', 'web-messaging.html#dom-messagechannel-port2', 'port2')}}</td>
   <td>{{Spec2('HTML WHATWG')}}</td>
   <td> </td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</h2>

{{Compat("api.MessageChannel.port2")}}

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="/en-US/docs/Web/API/Channel_Messaging_API/Using_channel_messaging">Using channel messaging</a></li>
</ul>