# withLatestFrom

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

## Also provide the last value from another observable.

:bulb: If you want the last emission any time a variable number of observables emits, try [combinelatest](combinelatest)!

### 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/) )

```javascript
// 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/) )

```javascript
// 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](../../recipes/progressbar)
* [Game Loop](../../recipes/gameloop)
* [Space Invaders Game](../../recipes/space-invaders-game)
* [Uncover Image Game](../../recipes/uncover-image-game)

### Additional Resources

*   [withLatestFrom](https://rxjs.dev/api/operators/withLatestFrom)

    :newspaper: - Official docs
*   [Combination operator: withLatestFrom](https://egghead.io/lessons/rxjs-combination-operator-withlatestfrom?course=rxjs-beyond-the-basics-operators-in-depth)

    :video\_camera: :dollar: - André Staltz

> :file\_folder: Source Code: [https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/withLatestFrom.ts](https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/withLatestFrom.ts)
