distinctUntilKeyChanged

signature: distinctUntilKeyChanged(key, compare: fn): Observable
Only emit when the specified key value has changed
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Examples
Example 1: Compare based on key
( StackBlitz )
// 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 )
// 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​
📰 - Official docs
📁 Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/distinctUntilKeyChanged.ts​

distinctUntilChanged

filter

Last modified 3yr ago