Observable9.ts

const source = (subscriber: Observer<string>) => {
  const socket = new WebSocket('wss://echo.websocket.org');
 
  socket.onopen = () => {
    socket.send('Hello, World!');
  };
 
  socket.onmessage = (e) => {
    subscriber.next(e.data);
  };
 
  socket.onclose = (e) => {
    if (e.wasClean) {
      subscriber.complete();
    } else {
      subscriber.error(new Error('Socket closed dirty!'));
    }
  };
 
  return () => {
    if (socket.readyState <= WebSocket.OPEN) {
      socket.close();
    }
  };
};
 
const teardown = source({
  next: console.log,
  complete: () => console.log('done'),
  error: console.error,
});
 
// Decide you really don't want to keep the socket open.
teardown();