EventSource

Server-Sent Events client. Opens a long-lived HTTP connection to a URL that streams text/event-stream frames, dispatches typed events on the EventSource, and reconnects automatically on disconnect with the last event ID.

Global

Global	Type
EventSource	class

API

const src = new EventSource('https://example.com/events');
src.onmessage = (ev) => console.log('default', ev.data);
src.addEventListener('update', (ev) => console.log('update', ev.data));
src.onerror = () => console.log('reconnecting…');
// src.close();   // stop receiving

Member	Description
new EventSource(url, init?)	Connect; init.withCredentials controls credentials
onmessage	Default-channel event handler
addEventListener(type, fn)	Named-event subscription (parsed from event: lines)
close()	Stop receiving and abort reconnection
readyState	0 connecting, 1 open, 2 closed

Notes

• Reconnection respects the server's retry: field if present; otherwise a default delay is used.
• The Last-Event-ID header carries the last received id: so the server can resume the stream.