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EventSource: message event

files/en-us/web/api/eventsource/message_event/index.md

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{{APIRef("Server Sent Events")}}{{AvailableInWorkers}}

The message event of the {{domxref("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 {{domxref("EventTarget.addEventListener", "addEventListener()")}}, or set an event handler property.

js-nolint
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

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.

js
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

js
evtSource.onmessage = (e) => {
  const newElement = document.createElement("li");

  newElement.textContent = `message: ${e.data}`;
  eventList.appendChild(newElement);
};

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also