MessagePort
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2015.
Note: This feature is available in Web Workers.
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.
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Disconnects the port, so it is no longer active.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
Inherits events from its parent, EventTarget.
message-
Fired when a
MessagePortobject receives a message. messageerror-
Fired when a
MessagePortobject 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
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Browser compatibility
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MessagePort
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close
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message event
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messageerror event
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postMessage
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options.includeUserActivation parameter
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start
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Available in workers
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Legend
Tip: you can click/tap on a cell for more information.
- Full support
- Full support
- Partial support
- Partial support
- No support
- No support
- Non-standard. Check cross-browser support before using.
- See implementation notes.
- Has more compatibility info.