throttle

signature: throttle(durationSelector: function(value): Observable | Promise): Observable

Emit value only when duration, determined by provided function, has passed.

Examples

Example 1: Throttle for 2 seconds, based on second observable

( jsBin |
jsFiddle )

import { interval } from 'rxjs/observable/interval';
import { throttle } from 'rxjs/operators';
//emit value every 1 second
const source = interval(1000);
//throttle for 2 seconds, emit latest value
const example = source.pipe(throttle(val => interval(2000)));
//output: 0...3...6...9
const subscribe = example.subscribe(val => console.log(val));

Example 2: Throttle with promise

( jsBin |
jsFiddle )

import { interval } from 'rxjs/observable/interval';
import { throttle, map } from 'rxjs/operators';
//emit value every 1 second
const source = interval(1000);
//incrementally increase the time to resolve based on source
const promise = val =>
  new Promise(resolve =>
    setTimeout(() => resolve(`Resolved: ${val}`), val * 100)
  );
//when promise resolves emit item from source
const example = source
  .pipe(
    throttle(promise),
    map(val => `Throttled off Promise: ${val}`);
  );
const subscribe = example.subscribe(val => console.log(val));

Additional Resources

• throttle
  - Official docs
• Filtering operator: throttle and throttleTime
  - André Staltz

Source Code:
https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/throttle.ts