EventSource: open event

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

Bubbles No
Cancelable No
Interface Event
Event handler property EventSource.onopen


var 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.");


Specification Status
HTML Living Standard
The definition of 'open event' in that specification.
Living Standard

Browser compatibility

No compatibility data found. Please contribute data for "api.EventSource.open_event" (depth: 1) to the MDN compatibility data repository.

See also

Document Tags and Contributors

Last updated by: chrisdavidmills,