EventSource: open 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.

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Note: This feature is available in Web Workers.

The open event of the EventSource interface is fired when a connection with an event source is opened.

This event is not cancelable and does not bubble.

Syntax

Use the event name in addEventListener():

addEventListener("open", (event) => { })

Alternatively, assign to the event handler property of the interface:

onopen = (event) => { }

Event type

A generic Event.

Examples

const evtSource = new EventSource("sse.php");

// addEventListener version
evtSource.addEventListener("open", (e) => {
  console.log("The connection has been established.");
});

// onopen version (but note that this replaces other event listeners
// added using onopen, if any)
evtSource.onopen = (e) => {
  console.log("The connection has been established.");
};