To enable servers to push data to Web pages over HTTP or using dedicated server-push protocols, this specification (non-normative) introduces the EventSource.
https://html.spec.whatwg.org/multipage/comms.html#server-sent-events
Browsers support: Chrome 6+, Chrome for Android 47+, Firefox 6+, iOS Safari 4.0-4.1+, Android Browser 4.4+, Safari 5+, Opera 11+