[RxJS] Subscription add()

You can use subsciprtion.add(anotherSubscription)to combine subscriptions and cancel them at the same time.

import { Observable } from 'rxjs';

const observer = {
  next: value => console.log('next', value),
  error: error => console.log('error', error),
  complete: () => console.log('complete!')
};

const observable = new Observable(subscriber => {
  let count = 0;

  const id = setInterval(() => {
    subscriber.next(count);
    count += 1;
  }, 1000);

  return () => {
    console.log('called');
    clearInterval(id);
  };
});

const subscription = observable.subscribe(observer);
const subscriptionTwo = observable.subscribe(observer);

/*
 * Subscriptions can be added together using the add method,
 * you can then unsubscribe to multiple at the same time.
 * This is simply personal preference, unsubscribing individually 
 * will produce the same result. Also, in future lessons, we will see how
 * to automate this unsubscribe process with operators.
 */
subscription.add(subscriptionTwo);

setTimeout(() => {
 /*
  * Note: Calling unsubscribe will not fire your complete callback,
  * but the returned function will be invoked cleaning up any
  * resources that were created by the subscription - in this
  * case the interval.
  */
  subscription.unsubscribe();
}, 3500);

Notice that, when you call subscription.unsubscribe(), the complete => ()function won't be triggered. 

complete: () => {}only get triggered, when we call subscriber.complete()