WebSocket: message event

The message event is fired when data is received through a WebSocket.


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

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

onmessage = (event) => {};

Event type

Event properties

In addition to the properties listed below, properties from the parent interface, Event, are available.

data Read only

The data sent by the message emitter.

origin Read only

A string representing the origin of the message emitter.

lastEventId Read only

A string representing a unique ID for the event.

source Read only

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

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).


// Create WebSocket connection.
const socket = new WebSocket("ws://localhost:8080");

// Listen for messages
socket.addEventListener("message", (event) => {
  console.log("Message from server ", event.data);


WebSockets Standard
# dom-websocket-onmessage

Browser compatibility

BCD tables only load in the browser

See also