# defer

#### signature: `defer(observableFactory: function(): SubscribableOrPromise): Observable`

## Create an observable with given subscription function.

***

💡 [`defer`](https://github.com/ReactiveX/rxjs/blob/ecc73d2a1564d0d3edffba90eec76510e509236c/src/internal/observable/iif.ts#L94-L100) is used as part of the [`iif`](https://www.learnrxjs.io/learn-rxjs/operators/conditional/iif) operator!

***

### Examples

**Example 1: Defer to get current date/time at the time of subscription**

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

```js
// RxJS v6+
import { defer, of, timer, merge } from 'rxjs';
import { switchMap } from 'rxjs/operators';

const s1 = of(new Date()); //will capture current date time
const s2 = defer(() => of(new Date())); //will capture date time at the moment of subscription

console.log(new Date());

timer(2000)
  .pipe(switchMap(_ => merge(s1, s2)))
  .subscribe(console.log);

/*
OUTPUT => 
2019-02-10T12:38:30.000Z (currrent date/time from first console log)
2019-02-10T12:38:30.000Z (date/time in s1 console log, captured date/time at the moment of observable creation)
2019-02-10T12:38:32.000Z (date/time in s2 console log, captured date/time at the moment of subscription)
*/

/*//NOTE: 'traditional' js equivalent of timer code above is:
setTimeout(() => {
  s1.subscribe(console.log);
  s2.subscribe(console.log);
}, 2000);
*/
```

### Related Recipes

* [Save Indicator](https://www.learnrxjs.io/learn-rxjs/recipes/save-indicator)

### Additional Resources

* [defer](https://rxjs.dev/api/index/function/defer) 📰 - Official docs

***

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


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