throttle.md

throttle

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

Emit value on the leading edge of an interval, but suppress new values until durationSelector has completed.

Examples

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

( StackBlitz | jsBin | jsFiddle )

// 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));

Example 2: Throttle with promise

( StackBlitz | jsBin | jsFiddle )

// 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));

Additional Resources

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

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