> 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/filtering/distinctuntilkeychanged.md).

# distinctUntilKeyChanged

#### signature: `distinctUntilKeyChanged(key, compare: fn): Observable`

## Only emit when the specified key value has changed

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

### Examples

**Example 1: Compare based on key**

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

```js
// RxJS v6+
import { from } from 'rxjs';
import { distinctUntilKeyChanged } 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 based on name property
  .pipe(distinctUntilKeyChanged('name'))
  // output: { name: 'Brian }, { name: 'Joe' }, { name: 'Sue' }
  .subscribe(console.log);
```

**Example 2: Keyboard events**

( [StackBlitz](https://stackblitz.com/edit/rxjs-distinctuntilkeychanged?file=index.ts\&devtoolsheight=50) )

```js
// RxJS v6+
import { fromEvent } from 'rxjs';
import { distinctUntilKeyChanged, pluck } from 'rxjs/operators';

const keys$ = fromEvent(document, 'keyup').pipe(
  distinctUntilKeyChanged < KeyboardEvent > 'code',
  pluck('key')
);

keys$.subscribe(console.log);
```

### Additional Resources

* [distinctUntilKeyChanged](https://rxjs.dev/api/operators/distinctUntilKeyChanged) 📰 - Official docs

***

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