EventSource: message event

Syntax

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

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

Event type

A MessageEvent. Inherits from Event.

Event properties

This interface also inherits properties from its parent, Event.

MessageEvent.data 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).

Examples

In this basic example, an EventSource is created to receive events from the server; a page with the name sse.php is responsible for generating the events.

const evtSource = new EventSource("sse.php");
const eventList = document.querySelector("ul");
evtSource.addEventListener("message", (e) => {
  const newElement = document.createElement("li");
  newElement.textContent = `message: ${e.data}`;
  eventList.appendChild(newElement);
});

onmessage equivalent

evtSource.onmessage = (e) => {
  const newElement = document.createElement("li");
  newElement.textContent = `message: ${e.data}`;
  eventList.appendChild(newElement);
};

Specifications

Browser compatibility

See also

• Using server-sent events
• open
• error