# delay

#### signature: `delay(delay: number | Date, scheduler: Scheduler): Observable`

## Delay emitted values by given time.

### Why use `delay`?

This operator is your go-to when simulating real-world scenarios such as network latency or introducing a pause before a value is emitted. The `delay` operator allows you to hold back values for a specified duration before they're released to subscribers.

Keep in mind that **`delay` won’t prevent the original observable from emitting values**. It merely postpones the delivery to its subscribers. This is a *gotcha* as it could look like your data is lagging or not in sync with the source, especially when multiple observables are at play.

### Examples

**Example 1: Delay to recognize long press**

( [StackBlitz](https://stackblitz.com/edit/rxjs-bru5fi?devtoolsheight=60) )

```js
import { fromEvent, of } from 'rxjs';
import { mergeMap, delay, takeUntil } from 'rxjs/operators';

const mousedown$ = fromEvent(document, 'mousedown');
const mouseup$ = fromEvent(document, 'mouseup');

mousedown$
  .pipe(mergeMap(event => of(event).pipe(delay(700), takeUntil(mouseup$))))
  .subscribe(event => console.log('Long Press!', event));
```

**Example 2: Delay for increasing durations**

( [StackBlitz](https://stackblitz.com/edit/typescript-twjn8r?file=index.ts\&devtoolsheight=100) )

```js
// RxJS v6+
import { of, merge } from 'rxjs';
import { mapTo, delay } from 'rxjs/operators';

//emit one item
const example = of(null);
//delay output of each by an extra second
const message = merge(
  example.pipe(mapTo('Hello')),
  example.pipe(mapTo('World!'), delay(1000)),
  example.pipe(mapTo('Goodbye'), delay(2000)),
  example.pipe(mapTo('World!'), delay(3000))
);
//output: 'Hello'...'World!'...'Goodbye'...'World!'
const subscribe = message.subscribe(val => console.log(val));
```

### Related Recipes

* [Battleship Game](https://www.learnrxjs.io/learn-rxjs/recipes/battleship-game)
* [Progress Bar](https://www.learnrxjs.io/learn-rxjs/recipes/progressbar)
* [Save Indicator](https://www.learnrxjs.io/learn-rxjs/recipes/save-indicator)
* [Swipe To Refresh](https://www.learnrxjs.io/learn-rxjs/recipes/swipe-to-refresh)

### Additional Resources

* [delay](https://rxjs.dev/api/operators/delay) 📰 - Official docs
* [Transformation operator: delay and delayWhen](https://egghead.io/lessons/rxjs-transformation-operators-delay-and-delaywhen?course=rxjs-beyond-the-basics-operators-in-depth) 🎥 💵 - André Staltz

***

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


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