# withLatestFrom

#### signature: `withLatestFrom(other: Observable, project: Function): Observable`

## Also provide the last value from another observable.

***

💡 If you want the last emission any time a variable number of observables emits, try [combinelatest](/ko.learn-rxjs/rxjs/operators/combination/combinelatest.md)!

***

[![Ultimate RxJS](https://drive.google.com/uc?export=view\&id=1qq2-q-eVe-F_-d0eSvTyqaGRjpfLDdJz)](https://ultimatecourses.com/courses/rxjs?ref=4)

### Examples

**Example 1: Latest value from quicker second source**

( [StackBlitz](https://stackblitz.com/edit/typescript-tznzbj?file=index.ts\&devtoolsheight=100) | [jsBin](http://jsbin.com/fitekeseru/1/edit?js,console) | [jsFiddle](https://jsfiddle.net/btroncone/9c3pfgpk/) )

```js
// RxJS v6+
import { withLatestFrom, map } from 'rxjs/operators';
import { interval } from 'rxjs';

//emit every 5s
const source = interval(5000);
//emit every 1s
const secondSource = interval(1000);
const example = source.pipe(
  withLatestFrom(secondSource),
  map(([first, second]) => {
    return `First Source (5s): ${first} Second Source (1s): ${second}`;
  })
);
/*
  "First Source (5s): 0 Second Source (1s): 4"
  "First Source (5s): 1 Second Source (1s): 9"
  "First Source (5s): 2 Second Source (1s): 14"
  ...
*/
const subscribe = example.subscribe(val => console.log(val));
```

**Example 2: Slower second source**

( [StackBlitz](https://stackblitz.com/edit/typescript-gigsdv?file=index.ts\&devtoolsheight=100) | [jsBin](http://jsbin.com/vujekucuxa/1/edit?js,console) | [jsFiddle](https://jsfiddle.net/btroncone/bywLL579/) )

```js
// RxJS v6+
import { withLatestFrom, map } from 'rxjs/operators';
import { interval } from 'rxjs';

//emit every 5s
const source = interval(5000);
//emit every 1s
const secondSource = interval(1000);
//withLatestFrom slower than source
const example = secondSource.pipe(
  //both sources must emit at least 1 value (5s) before emitting
  withLatestFrom(source),
  map(([first, second]) => {
    return `Source (1s): ${first} Latest From (5s): ${second}`;
  })
);
/*
  "Source (1s): 4 Latest From (5s): 0"
  "Source (1s): 5 Latest From (5s): 0"
  "Source (1s): 6 Latest From (5s): 0"
  ...
*/
const subscribe = example.subscribe(val => console.log(val));
```

### Related Recipes

* [Progress Bar](/ko.learn-rxjs/rxjs/recipes/progressbar.md)
* [Game Loop](/ko.learn-rxjs/rxjs/recipes/gameloop.md)
* [Space Invaders Game](/ko.learn-rxjs/rxjs/recipes/space-invaders-game.md)
* [Uncover Image Game](/ko.learn-rxjs/rxjs/recipes/uncover-image-game.md)

### Additional Resources

* [withLatestFrom](https://rxjs.dev/api/operators/withLatestFrom) 📰 - Official docs
* [withLatestFrom](https://indepth.dev/reference/rxjs/operators/with-latest-from) - In Depth Dev Reference
* [Combination operator: withLatestFrom](https://egghead.io/lessons/rxjs-combination-operator-withlatestfrom?course=rxjs-beyond-the-basics-operators-in-depth) 🎥 💵 - André Staltz

***

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


---

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