EventSource: open event

{{APIRef("Server Sent Events")}}{{AvailableInWorkers}}

The open event of the {{domxref("EventSource")}} interface is fired when a connection with an event source is opened.

This event is not cancelable and does not bubble.

Syntax

Use the event name in methods like {{domxref("EventTarget.addEventListener", "addEventListener()")}}, or set an event handler property.

addEventListener("open", (event) => { })

onopen = (event) => { }

Event type

A generic {{domxref("Event")}}.

Examples

const 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.");
};

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• Using server-sent events
• {{domxref("EventSource/error_event", "error")}}
• {{domxref("EventSource/message_event", "message")}}