DistinctUntilKeyChanged

Returns an Observable that emits all items emitted by the source Observable that are distinct by comparison from the previous item, using a property accessed by using the key provided to check if the two items are distinct.

Syntax

distinctUntilKeyChanged<T, K extends keyof T>(key: K, compare?: (x: T[K], y: T[K]) => boolean): MonoTypeOperatorFunction<T>

Parameters	Description
key	String key for object property lookup on each item.
defaultValue Optional	Default is undefined. Comparison function called to test if an item is distinct from the previous item in the source.

Returns

MonoTypeOperatorFunction: A function that returns an Observable that emits items from the source Observable with distinct values based on the key specified.

Example

import { of } from 'rxjs';
import { distinctUntilKeyChanged } from 'rxjs/operators';
 
 interface Person {
    age: number,
    name: string
 }
 
of(
    { age: 4, name: 'Foo'},
    { age: 7, name: 'Bar'},
    { age: 5, name: 'Foo'},
    { age: 6, name: 'Foo'},
  ).pipe(
    distinctUntilKeyChanged('name'),
  )
  .subscribe(x => console.log(x));
 
// displays:
// { age: 4, name: 'Foo' }
// { age: 7, name: 'Bar' }
// { age: 5, name: 'Foo' }