# timer

#### signature: `timer(initialDelay: number | Date, period: number, scheduler: Scheduler): Observable`

## After given duration, emit numbers in sequence every specified duration.

### Examples

**Example 1: timer emits 1 value then completes**

( [StackBlitz](https://stackblitz.com/edit/typescript-fvkzgg?file=index.ts\&devtoolsheight=100) | [jsBin](http://jsbin.com/pazajanehu/1/edit?js,console) | [jsFiddle](https://jsfiddle.net/btroncone/vpx0y8fu/) )

```js
// RxJS v6+
import { timer } from 'rxjs';

//emit 0 after 1 second then complete, since no second argument is supplied
const source = timer(1000);
//output: 0
const subscribe = source.subscribe(val => console.log(val));
```

**Example 2: timer emits after 1 second, then every 2 seconds**

( [StackBlitz](https://stackblitz.com/edit/typescript-h9pzxr?file=index.ts\&devtoolsheight=100) | [jsBin](http://jsbin.com/kejidofuje/1/edit?js,console) | [jsFiddle](https://jsfiddle.net/btroncone/30ddov8j/) )

```js
// RxJS v6+
import { timer } from 'rxjs';

/*
  timer takes a second argument, how often to emit subsequent values
  in this case we will emit first value after 1 second and subsequent
  values every 2 seconds after
*/
const source = timer(1000, 2000);
//output: 0,1,2,3,4,5......
const subscribe = source.subscribe(val => console.log(val));
```

### Related Recipes

* [HTTP Polling](/learn-rxjs/recipes/http-polling.md)

### Additional Resources

* [timer](https://rxjs.dev/api/index/function/timer) 📰 - Official docs
* [Creation operators: interval and timer](https://egghead.io/lessons/rxjs-creation-operators-interval-and-timer?course=rxjs-beyond-the-basics-creating-observables-from-scratch) 🎥 💵 - André Staltz

***

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


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