distinctUntilChanged

signature: distinctUntilChanged(compare: function): Observable
Only emit when the current value is different than the last.
💡 distinctUntilChanged uses === comparison by default, object references must match!
💡 If you want to compare based on an object property, you can use distinctUntilKeyChanged instead!
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Examples
Example 1: distinctUntilChanged with basic values
( StackBlitz )
// 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 )
// 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 )
// 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​
​Save Indicator​
​Type Ahead​
Additional Resources
​distinctUntilChanged​
📰 - Official docs
​Filtering operator: distinct and distinctUntilChanged​
🎥 💵 - André Staltz
📁 Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/distinctUntilChanged.ts​
distinct
distinctUntilKeyChanged
Last updated 5 months ago