Window: message event

The message event is fired on a Window object when the window receives a message, for example from a call to Window.postMessage() from another browsing context.

This event is not cancellable and does not bubble.


Use the event name in methods like addEventListener(), or set an event handler property.

addEventListener("message", (event) => {});

onmessage = (event) => {};

Event type

Event properties

This interface also inherits properties from its parent, Event. Read only

The data sent by the message emitter.

MessageEvent.origin Read only

A string representing the origin of the message emitter.

MessageEvent.lastEventId Read only

A string representing a unique ID for the event.

MessageEvent.source Read only

A MessageEventSource (which can be a WindowProxy, MessagePort, or ServiceWorker object) representing the message emitter.

MessageEvent.ports Read only

An array of MessagePort objects representing the ports associated with the channel the message is being sent through (where appropriate, e.g. in channel messaging or when sending a message to a shared worker).


Suppose a script sends a message to a different browsing context, such as another <iframe>, using code like this:

const targetFrame =[1];
const targetOrigin = "";
const windowMessageButton = document.querySelector("#window-message");

windowMessageButton.addEventListener("click", () => {
  targetFrame.postMessage("hello there", targetOrigin);

The receiver can listen for the message using addEventListener() with code like this:

window.addEventListener("message", (event) => {
  console.log(`Received message: ${}`);

Alternatively the listener could use the onmessage event handler property:

window.onmessage = (event) => {
  console.log(`Received message: ${}`);


HTML Standard
# event-message
HTML Standard
# handler-window-onmessage

Browser compatibility

BCD tables only load in the browser

See also