# distinctUntilChanged

#### signature: `distinctUntilChanged(compare: function): Observable`

## Only emit when the current value is different than the last.

:bulb: distinctUntilChanged uses `===` comparison by default, object references must match!

:bulb: If you want to compare based on an object property, you can use [`distinctUntilKeyChanged`](/learn-rxjs-korean/learn-rxjs/recipes-1/filtering/distinctuntilkeychanged.md) instead!

### Examples

**Example 1: distinctUntilChanged with basic values**

( [StackBlitz](https://stackblitz.com/edit/typescript-bsb8mw?file=index.ts\&devtoolsheight=100) )

```javascript
// RxJS v6+
import { from } from 'rxjs';
import { distinctUntilChanged } from 'rxjs/operators';

// only output distinct values, based on the last emitted value
const source$ = from([1, 1, 2, 2, 3, 3]);

source$
  .pipe(distinctUntilChanged())
  // output: 1,2,3
  .subscribe(console.log);
```

**Example 2: distinctUntilChanged with objects**

( [StackBlitz](https://stackblitz.com/edit/typescript-moe7mh?file=index.ts\&devtoolsheight=100) )

```javascript
// RxJS v6+
import { from } from 'rxjs';
import { distinctUntilChanged } from 'rxjs/operators';

const sampleObject = { name: 'Test' };

//Objects must be same reference
const source$ = from([sampleObject, sampleObject, sampleObject]);

// only emit distinct objects, based on last emitted value
source$
  .pipe(distinctUntilChanged())
  // output: {name: 'Test'}
  .subscribe(console.log);
```

**Example 3: Using custom comparer function**

( [StackBlitz](https://stackblitz.com/edit/typescript-hzta27?file=index.ts\&devtoolsheight=100) )

```javascript
// RxJS v6+
import { from } from 'rxjs';
import { distinctUntilChanged } from 'rxjs/operators';

// only output distinct values, based on the last emitted value
const source$ = from([
  { name: 'Brian' },
  { name: 'Joe' },
  { name: 'Joe' },
  { name: 'Sue' }
]);

source$
  // custom compare for name
  .pipe(distinctUntilChanged((prev, curr) => prev.name === curr.name))
  // output: { name: 'Brian }, { name: 'Joe' }, { name: 'Sue' }
  .subscribe(console.log);
```

### Related Recipes

* [Lockscreen](/learn-rxjs-korean/learn-rxjs/recipes/lockscreen.md)
* \[Save Indicator]\('../../recipes/save-indicator.md)
* [Type Ahead](/learn-rxjs-korean/learn-rxjs/recipes/type-ahead.md)

### Additional Resources

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

  :newspaper: - Official docs
* [Filtering operator: distinct and distinctUntilChanged](https://egghead.io/lessons/rxjs-filtering-operators-distinct-and-distinctuntilchanged?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/distinctUntilChanged.ts>


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