Window: message event

{{APIRef}} 

The message event is fired on a {{domxref('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.

Syntax

Use the event name in methods like {{domxref("EventTarget.addEventListener", "addEventListener()")}} , or set an event handler property.

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

onmessage = (event) => {};

Event type

A {{domxref("MessageEvent")}} . Inherits from {{domxref("Event")}} .

{{InheritanceDiagram("MessageEvent")}} 

Event properties

This interface also inherits properties from its parent, {{domxref("Event")}} .

• {{domxref("MessageEvent.data")}}  {{ReadOnlyInline}} 
  • : The data sent by the message emitter.
• {{domxref("MessageEvent.origin")}}  {{ReadOnlyInline}} 
  • : A string representing the origin of the message emitter.
• {{domxref("MessageEvent.lastEventId")}}  {{ReadOnlyInline}} 
  • : A string representing a unique ID for the event.
• {{domxref("MessageEvent.source")}}  {{ReadOnlyInline}} 
  • : A MessageEventSource (which can be a {{glossary("WindowProxy")}} , {{domxref("MessagePort")}} , or {{domxref("ServiceWorker")}}  object) representing the message emitter.
• {{domxref("MessageEvent.ports")}}  {{ReadOnlyInline}} 
  • : An array of {{domxref("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).

Examples

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

const targetFrame = window.top.frames[1];
const targetOrigin = "https://example.org";
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: ${event.data}`);
});

Alternatively the listener could use the onmessage event handler property:

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

Specifications

{{Specifications}} 

Browser compatibility

{{Compat}} 

See also

• Related events: messageerror.
• Window.postMessage().