I try to implement a countdown timer in angular 6 using rxjs 6. I also need to be able to subscribe to results and to reset the timer:

What I tried:

var timer =  interval(1000).pipe(
take(4)
);
timer.subscribe(x => console.log(x));

Result:

0
1
2
3

What I need is to reverse the timer to count from 3 to 1

I found this coundown function to implement reverse count, but I cannot subscribe to it, like in first example

 interval(1000).pipe(
 map((x) => { console.log( x) })
  );

Result:

empty

I try to implement a countdown timer in angular 6 using rxjs 6. I also need to be able to subscribe to results and to reset the timer:

What I tried:

var timer =  interval(1000).pipe(
take(4)
);
timer.subscribe(x => console.log(x));

Result:

0
1
2
3

What I need is to reverse the timer to count from 3 to 1

I found this coundown function to implement reverse count, but I cannot subscribe to it, like in first example

 interval(1000).pipe(
 map((x) => { console.log( x) })
  );

Result:

empty

• javascript
• angular
• rxjs
• countdowntimer

3 Answers 3

You can use timer instead of interval, to actually implement the countdown you should map the timer result like this: map(i => countdownStart - i)

  const countdownStart = 3;

  Rx.Observable
    .timer(1000, 1000)
    .map(i =>  countdownStart - i)
    .take(countdownStart + 1)
    .subscribe(i => console.log(i));

Logs: 3 2 1 0

Another possible solution is to use the range operator.

Rx.Observable
  .range(0, countdownStart + 1)
  .map(i => countdownStart - i)
  .subscribe(i => console.log(i));

Logs: 3 2 1 0

Here is how I do it with TimerObservable. Remember to unsubscribe on destroy.

import {TimerObservable} from "rxjs/observable/TimerObservable";
import { Subscription } from 'rxjs';

export class MyComponent implements OnInit, OnDestroy {

    private sub: Subscription;

    ngOnInit() {
        // Delay 0 seconds, run every second
        let timer = TimerObservable.create(0, 1000);

        let number = 3;

        this.sub = timer.subscribe(t => {
            if(number !== 0) {
               console.log(number);
               number--;
            }
        });
    }

    ngOnDestroy(): void {
        this.sub.unsubscribe();
    }
}

How about?

var timer =  interval(1000).pipe(
  take(4),
  map(x => 3 - x)
);
timer.subscribe(console.log);