app.js

// rxjs is global variable
const lg = console.log

const observable = new rxjs.Observable((subscriber) => {
  console.log('Hi')
  subscriber.next(1);
  subscriber.next(2);
  subscriber.next(3);
  setTimeout(() => {
    subscriber.next(4);
    subscriber.complete();
  }, 1000);
});

console.log('just before subscribe');
observable.subscribe({
  next(x) {
    console.log('got value ' + x);
  },
  error(err) {
    console.error('something wrong occurred: ' + err);
  },
  complete() {
    console.log('done');
  },
});
observable.subscribe((x)=>{
  console.log('x:', x)
})
observable.subscribe((y)=>{
  console.log('y:',y)
})
console.log('just after subscribe');

lg('-------------------')

const observable2 = rxjs.from([10, 20, 30]);
const subscription2 = observable2.subscribe((x) => console.log(x));
// Later:
subscription2.unsubscribe();

lg('-------------------')