EventSource: message event
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since January 2020.
Note: This feature is available in Web Workers.
The message
event of the EventSource
interface is fired when data is received through an event source.
This event is not cancelable and does not bubble.
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
, orServiceWorker
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
Specification |
---|
HTML Standard # event-message |
HTML Standard # handler-eventsource-onmessage |
Browser compatibility
BCD tables only load in the browser