# 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](https://stackblitz.com/edit/typescript-pfcmjw?file=index.ts\&devtoolsheight=100) | [jsBin](http://jsbin.com/wohefujipo/1/edit?js,console) | [jsFiddle](https://jsfiddle.net/btroncone/h8na4m0p/) )

```js
// 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](https://stackblitz.com/edit/typescript-g74v3q?file=index.ts\&devtoolsheight=100) | [jsBin](http://jsbin.com/seyaguwunu/1/edit?js,console) | [jsFiddle](https://jsfiddle.net/btroncone/w5Lbzz9f/) )

```js
// 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](https://rxjs.dev/api/operators/throttle) 📰 - Official docs
* [Filtering operator: throttle and throttleTime](https://egghead.io/lessons/rxjs-filtering-operators-throttle-and-throttletime?course=rxjs-beyond-the-basics-operators-in-depth) 🎥 💵 - André Staltz

***

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