Subscription

What is a Subscription? A Subscription is an object that represents a disposable resource, usually the execution of an Observable. A Subscription has one important method, unsubscribe, that takes no argument and just disposes the resource held by the subscription. In previous versions of RxJS, Subscription was called "Disposable".

import { interval } from 'rxjs';

const observable = interval(1000);
const subscription = observable.subscribe(x => console.log(x));
// Later:
// This cancels the ongoing Observable execution which
// was started by calling subscribe with an Observer.
subscription.unsubscribe();

A Subscription essentially just has an unsubscribe() function to release resources or cancel Observable executions.

Subscriptions can also be put together, so that a call to an unsubscribe() of one Subscription may unsubscribe multiple Subscriptions. You can do this by "adding" one subscription into another:

import { interval } from 'rxjs';

const observable1 = interval(400);
const observable2 = interval(300);

const subscription = observable1.subscribe(x => console.log('first: ' + x));
const childSubscription = observable2.subscribe(x => console.log('second: ' + x));

subscription.add(childSubscription);

setTimeout(() => {
  // Unsubscribes BOTH subscription and childSubscription
  subscription.unsubscribe();
}, 1000);

When executed, we see in the console:

second: 0
first: 0
second: 1
first: 1
second: 2

Subscriptions also have a remove(otherSubscription) method, in order to undo the addition of a child Subscription.