// RxJS v6+
import { interval } from 'rxjs';
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));

// RxJS v6+
import { interval } from 'rxjs';
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));