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

ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
open eventChrome Full support 6Edge Full support 79Firefox Full support 6IE No support NoOpera Full support YesSafari Full support 5WebView Android Full support YesChrome Android Full support 18Firefox Android Full support 45Opera Android Full support 12Safari iOS Full support 5Samsung Internet Android Full support 1.0


Full support
Full support
No support
No support

See also