MessagePort
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.
MessagePort
is a transferable object.
Note: This feature is available in Web Workers
Instance 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 usingonmessage
). close()
-
Disconnects the port, so it is no longer active.
Events
message
-
Fired when a
MessagePort
object receives a message. messageerror
-
Fired when a
MessagePort
object receives a message that can't be deserialized.
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.
js
const channel = new MessageChannel();
const output = document.querySelector(".output");
const 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 |
---|
HTML Standard # message-ports |
Browser compatibility
BCD tables only load in the browser