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.

Syntax

eventSource.onopen = function

Examples

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

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

Specifications

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

Browser compatibility

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari
EventSource support 6 No support 6.0 (6.0) No support (Yes) 5
Available in shared and dedicated workers[1] (Yes) No support 53.0 (53.0) No support (Yes) (Yes)
Feature Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
EventSource support 4.4 45 No support 12 4.1
Available in shared and dedicated workers[1] (Yes) 53.0 (53.0) No support (Yes) (Yes)

[1] But not service workers as yet.

See also

Document Tags and Contributors

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