MessagePort 接口的 onmessage 事件处理程序是一个 EventListener, 当在端口上触发一个类型为 messageMessageEvent 时被调用 - 即,当端口接收到消息时。

备注: 此特性在 Web Worker 中可用。


channel.onmessage = function() { ... };


In the following code block, you can see a new channel being created using the MessageChannel.MessageChannel constructor. When the IFrame has loaded, we pass MessageChannel.port2 to the IFrame using MessagePort.postMessage (en-US) along with a message. The handleMessage handler then responds to a message being sent back from the IFrame using onmessage, putting it into a paragraph — MessageChannel.port1 is listened to, to check when the message arrives.

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 =;

For a full working example, see our channel messaging basic demo on Github (run it live too).


HTML Standard
# event-message
HTML Standard
# handler-messageport-onmessage

Browser compatibility

BCD tables only load in the browser

See also