EventSource: withCredentials property
  The withCredentials read-only property of the
  EventSource interface returns a boolean value indicating whether
  the EventSource object was instantiated with CORS credentials set.
Value
  A boolean value indicating whether the EventSource object was
  instantiated with CORS credentials set (true), or not (false,
  the default).
Examples
js
const evtSource = new EventSource("sse.php");
console.log(evtSource.withCredentials);
Note: You can find a full example on GitHub — see Simple SSE demo using PHP.
Specifications
| Specification | 
|---|
| HTML Standard  # dom-eventsource-withcredentials-dev  | 
Browser compatibility
BCD tables only load in the browser