The lift method on each source hides away the internals of RxJS so you can simply connect a source to the subscriber you're working with. The lift method take an object with a call function with subscriber and source arguments, then it's up to you how you want to connect them together.

 

Previous we created a custom subscriber, we do it in subscribe() function:

import { from, Subscriber } from "rxjs";const observable$ = from([1, 2, 3, 4, 5]);const subscriber = {  next: value => {    console.log(value);  },  complete: () => {    console.log("done");  },  error: value => {    console.log(value);  }};class DoulbeSubscriber extends Subscriber {  _next(value) {    this.destination.next(value * 2);  }}observable$.subscribe(new DoulbeSubscriber(subscriber));

 

Of course it isn't ideal to do the transformation in subscriber.

Better way is that we can do though `pipe`, create a custom subscriber and using in the pipe:

const doulbe = source => {  return source.lift({    call(sub, source) {      source.subscribe(new DoulbeSubscriber(sub));    }  });};observable$.pipe(doulbe).subscribe(subscriber);

 

We can use `lift` function which accpet an object has a call(subscriber, source).