> For the complete documentation index, see [llms.txt](https://chasethestar.gitbook.io/ko.learn-rxjs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://chasethestar.gitbook.io/ko.learn-rxjs/rxjs/operators/combination/startwith.md).

# startWith

#### signature: `startWith(an: Values): Observable`

## Emit given value first.

***

💡 A [BehaviorSubject](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/subjects/behaviorsubject.md) can also start with an initial value!

***

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

### Examples

( [example tests](https://github.com/btroncone/learn-rxjs/blob/master/operators/specs/combination/startwith-spec.ts) )

**Example 1: startWith on number sequence**

( [StackBlitz](https://stackblitz.com/edit/typescript-2qrwjt?file=index.ts\&devtoolsheight=100) | [jsBin](http://jsbin.com/lezuravizu/1/edit?js,console) | [jsFiddle](https://jsfiddle.net/btroncone/e8dn3ggp/) )

```js
// RxJS v6+
import { startWith } from 'rxjs/operators';
import { of } from 'rxjs';

//emit (1,2,3)
const source = of(1, 2, 3);
//start with 0
const example = source.pipe(startWith(0));
//output: 0,1,2,3
const subscribe = example.subscribe(val => console.log(val));
```

**Example 2: startWith for initial scan value**

( [StackBlitz](https://stackblitz.com/edit/typescript-8gkbsc?file=index.ts\&devtoolsheight=100) | | [jsBin](http://jsbin.com/gemevuzoha/1/edit?js,console) | [jsFiddle](https://jsfiddle.net/btroncone/54r3g83e/) )

```js
// RxJS v6+
import { startWith, scan } from 'rxjs/operators';
import { of } from 'rxjs';

//emit ('World!', 'Goodbye', 'World!')
const source = of('World!', 'Goodbye', 'World!');
//start with 'Hello', concat current string to previous
const example = source.pipe(
  startWith('Hello'),
  scan((acc, curr) => `${acc} ${curr}`)
);
/*
  output:
  "Hello"
  "Hello World!"
  "Hello World! Goodbye"
  "Hello World! Goodbye World!"
*/
const subscribe = example.subscribe(val => console.log(val));
```

**Example 3: startWith multiple values**

( [StackBlitz](https://stackblitz.com/edit/typescript-ek45ff?file=index.ts\&devtoolsheight=100) | [jsBin](http://jsbin.com/cumupemuxa/1/edit?js,console) | [jsFiddle](https://jsfiddle.net/btroncone/ckcyj3ms/) )

```js
// RxJS v6+
import { startWith } from 'rxjs/operators';
import { interval } from 'rxjs';

//emit values in sequence every 1s
const source = interval(1000);
//start with -3, -2, -1
const example = source.pipe(startWith(-3, -2, -1));
//output: -3, -2, -1, 0, 1, 2....
const subscribe = example.subscribe(val => console.log(val));
```

### Related Recipes

* [Alphabet Invasion Game](/ko.learn-rxjs/rxjs/recipes/alphabet-invasion-game.md)
* [Breakout Game](/ko.learn-rxjs/rxjs/recipes/breakout-game.md)
* [Car Racing Game](/ko.learn-rxjs/rxjs/recipes/car-racing-game.md)
* [Platform Jumper Game](/ko.learn-rxjs/rxjs/recipes/platform-jumper-game.md)
* [Smart Counter](/ko.learn-rxjs/rxjs/recipes/smartcounter.md)
* [Space Invaders Game](/ko.learn-rxjs/rxjs/recipes/space-invaders-game.md)
* [Stop Watch](/ko.learn-rxjs/rxjs/recipes/stop-watch.md)
* [Tank Battle Game](/ko.learn-rxjs/rxjs/recipes/tank-battle-game.md)
* [Tetris Game](/ko.learn-rxjs/rxjs/recipes/tetris-game.md)
* [Uncover Image Game](/ko.learn-rxjs/rxjs/recipes/uncover-image-game.md)

### Additional Resources

* [startWith](https://rxjs.dev/api/operators/startWith) 📰 - Official docs
* [Displaying initial data with startWith](https://egghead.io/lessons/rxjs-displaying-initial-data-with-startwith?course=step-by-step-async-javascript-with-rxjs) 🎥 💵 - John Linquist
* [Clear data while loading with startWith](https://egghead.io/lessons/rxjs-reactive-programming-clear-data-while-loading-with-rxjs-startwith?course=introduction-to-reactive-programming) 🎥 💵 - André Staltz
* [Combination operator: concat, startWith](https://egghead.io/lessons/rxjs-combination-operators-concat-startwith?course=rxjs-beyond-the-basics-operators-in-depth) 🎥 💵 - André Staltz

***

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


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