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distinctUntilKeyChanged

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

Only emit when the specified key value has changed

Examples

Example 1: Compare based on key
// 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
// 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