EventSource: close() method
  The close() method of the EventSource
  interface closes the connection, if one is made, and sets the
  EventSource.readyState attribute to 2 (closed).
Note: If the connection is already closed, the method does nothing.
Syntax
js
close()
Parameters
None.
Return value
None (undefined).
Examples
js
const button = document.querySelector("button");
const evtSource = new EventSource("sse.php");
button.onclick = () => {
  console.log("Connection closed");
  evtSource.close();
};
Note: You can find a full example on GitHub — see Simple SSE demo using PHP.
Specifications
| Specification | 
|---|
| HTML Standard  # dom-eventsource-close-dev  | 
Browser compatibility
BCD tables only load in the browser