The onopen property of the EventSource interface is an EventHandler called when an open event is received, that is when the connection was just opened.


eventSource.onopen = function


evtSource.onopen = function() {
  console.log("Connection to server opened.");

Note: You can find a full example on GitHub — see Simple SSE demo using PHP.


Specification Status Comment
HTML Living Standard
The definition of 'onopen' in that specification.
Living Standard Initial definition

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support6 No6 No Yes5
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support618 No45125 ?

See also

Document Tags and Contributors

Contributors to this page: fscholz, Sheppy, chrisdavidmills
Last updated by: fscholz,