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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.
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- Disconnects the port, so it is no longer active.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
- An
EventListener
called when aMessageEvent
of typemessage
is fired on the port—that is, when the port receives a message. MessagePort.onmessageerror
- An
EventListener
called when aMessageEvent
of typeMessageError
is fired—that is, when it receives a message that cannot be deserialized.
Example
In the following example, you can see a new channel being created using the MessageChannel.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 simply 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
Desktop | Mobile | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Basic support | Chrome Full support 4 | Edge Full support Yes | Firefox Full support Yes | IE Full support 10 | Opera Full support 10.6 | Safari Full support 5 | WebView Android Full support Yes | Chrome Android Full support 18 | Edge Mobile Full support Yes | Firefox Android Full support Yes | Opera Android Full support 11.5 | Safari iOS Full support 5.1 | Samsung Internet Android ? |
Available in workers | Chrome Full support Yes | Edge ? | Firefox Full support 41 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile ? | Firefox Android Full support 41 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes |
close | Chrome Full support 4 | Edge Full support Yes | Firefox Full support Yes | IE Full support 10 | Opera Full support 10.6 | Safari Full support 5 | WebView Android Full support Yes | Chrome Android Full support 18 | Edge Mobile Full support Yes | Firefox Android No support No | Opera Android Full support 11.5 | Safari iOS Full support 5.1 | Samsung Internet Android ? |
onmessage | Chrome Full support 4 | Edge Full support Yes | Firefox Full support Yes | IE Full support 10 | Opera Full support 10.6 | Safari Full support 5 | WebView Android Full support Yes | Chrome Android Full support 18 | Edge Mobile Full support Yes | Firefox Android No support No | Opera Android Full support 11.5 | Safari iOS Full support 5.1 | Samsung Internet Android ? |
onmessageerror | Chrome Full support 60 | Edge ? | Firefox Full support 57 | IE ? | Opera Full support 47 | Safari ? | WebView Android Full support 60 | Chrome Android Full support 60 | Edge Mobile ? | Firefox Android Full support 57 | Opera Android Full support 47 | Safari iOS ? | Samsung Internet Android ? |
postMessage | Chrome Full support 4 | Edge Full support Yes | Firefox Full support Yes | IE Full support 10 | Opera Full support 10.6 | Safari Full support 5 | WebView Android Full support Yes | Chrome Android Full support 18 | Edge Mobile Full support Yes | Firefox Android No support No | Opera Android Full support 11.5 | Safari iOS Full support 5.1 | Samsung Internet Android ? |
start | Chrome Full support 4 | Edge Full support Yes | Firefox Full support Yes | IE Full support 10 | Opera Full support 10.6 | Safari Full support 5 | WebView Android Full support Yes | Chrome Android Full support 18 | Edge Mobile Full support Yes | Firefox Android No support No | Opera Android Full support 11.5 | Safari iOS Full support 5.1 | Samsung Internet Android ? |
Legend
- Full support
- Full support
- No support
- No support
- Compatibility unknown
- Compatibility unknown