The MessagePort
interface of the Channel Messaging API represents one of the two ports of a MessageChannel
, allowing sending of messages from one port and listening out for them arriving at the other.
Methods
Inherits methods from its parent, EventTarget
MessagePort.postMessage
- Sends a message from the port, and optionally, transfers ownership of objects to other browsing contexts.
MessagePort.start
- Starts the sending of messages queued on the port (only needed when using
EventTarget.addEventListener
; it is implied when usingMessagePort.onmessage
.) MessagePort.close
- Disconnects the port, so it is no longer active.
Event handlers
Inherits event handlers from its parent, EventTarget
MessagePort.onmessage
- Is an
EventListener
that is called whenever anMessageEvent
of typemessage
is fired on the port — that is, when the port receives a message.
Example
In the following code block, you can see a new channel being created using the MessageChannel.MessageChannel
constructor. When the IFrame has loaded, we transfer MessageChannel.port2
(a MessagePort
) to the IFrame using MessagePort.postMessage
along with a message. The handleMessage
handler then responds to a message being sent back from the IFrame (using MessagePort.onmessage
), putting it into a paragraph.
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; }
For a full working example, see our channel messaging basic demo on Github (run it live too).
Specifications
Specification | Status | Comment |
---|---|---|
WHATWG HTML Living Standard The definition of 'MessagePort' in that specification. |
Living Standard | No difference from HTML5 Web Messaging. |
HTML5 Web Messaging The definition of 'MessagePort' in that specification. |
Recommendation | W3C version of the spec |
Browser compatibility
Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|---|
Basic support | 4 | (Yes) | (Yes) | 10.0 | 10.6 | 5 |
Available in workers | (Yes) | ? | 41 (41) | (Yes) | (Yes) | (Yes) |
Feature | Android | Chrome for Android | Edge | Firefox Mobile (Gecko) | Firefox OS (Gecko) | IE Phone | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|---|---|
Basic support | 4.4 | 4 | (Yes) | No support | No support | 10.0 | 11.5 | 5.1 |
Available in workers | (Yes) | (Yes) | ? | 41.0 (41) | (Yes) | (Yes) | (Yes) | (Yes) |