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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.

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 methods like addEventListener(), or set an event handler property.

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

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
evtSource.onopen = (e) => {
  console.log("The connection has been established.");
};

Specifications

Specification
HTML> # event-open>
HTML> # handler-eventsource-onopen>

Browser compatibility