MessagePort - Web APIs 编辑
The MessagePort
interface of the Channel Messaging API represents one of the two ports of a MessageChannel
, allowing messages to be sent from one port and listening out for them arriving at the other.
Note:
This feature is available in Web Workers.Methods
Inherits methods from its parent, EventTarget
postMessage()
- Sends a message from the port, and optionally, transfers ownership of objects to other browsing contexts.
start()
- Starts the sending of messages queued on the port (only needed when using
EventTarget.addEventListener
; it is implied when usingMessagePort.onmessage
.) close()
- Disconnects the port, so it is no longer active.
Event handlers
Inherits event handlers from its parent, EventTarget
onmessage
- An
EventListener
called whenMessageEvent
of typemessage
is fired on the port—that is, when the port receives a message. onmessageerror
- An
EventListener
called when aMessageEvent
of typeMessageError
is fired—that is, when it receives a message that cannot be deserialized.
Events
message
- Fired when a
MessagePort
object receives a message.
Also available via theonmessage
property. messageerror
- Fired when a
MessagePort
object receives a message that can't be deserialized.
Also available via theonmessageerror
property.
Example
In the following example, you can see a new channel being created using the MessageChannel()
constructor.
When the IFrame has loaded, we register an onmessage
handler for MessageChannel.port1
and transfer MessageChannel.port2
to the IFrame using the window.postMessage
method along with a message.
When a message is received back from the IFrame, the onMessage
function outputs the message to a paragraph.
var channel = new MessageChannel(); var output = document.querySelector('.output'); var iframe = document.querySelector('iframe'); // Wait for the iframe to load iframe.addEventListener("load", onLoad); function onLoad() { // Listen for messages on port1 channel.port1.onmessage = onMessage; // Transfer port2 to the iframe iframe.contentWindow.postMessage('Hello from the main page!', '*', [channel.port2]); } // Handle messages received on port1 function onMessage(e) { output.innerHTML = e.data; }
For a full working example, see our channel messaging basic demo on Github (run it live too).
Specifications
Specification | Status | Comment |
---|---|---|
HTML Living Standard The definition of 'Message ports' in that specification. | Living Standard |
Browser compatibility
BCD tables only load in the browser
See also
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