@reactivex/rxjs/compat/operator/distinctUntilKeyChanged.ts

Reactive Extensions for modern JavaScript

import { Observable } from 'rxjs';
import { distinctUntilKeyChanged as higherOrder } from 'rxjs/operators';

/* tslint:disable:max-line-length */
export function distinctUntilKeyChanged<T>(this: Observable<T>, key: keyof T): Observable<T>;
export function distinctUntilKeyChanged<T, K extends keyof T>(this: Observable<T>, key: K, compare: (x: T[K], y: T[K]) => boolean): Observable<T>;
/* tslint:enable:max-line-length */

/**
 * 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.
 *
 * If a comparator function is provided, then it will be called for each item to test for whether or not that value should be emitted.
 *
 * If a comparator function is not provided, an equality check is used by default.
 *
 * @example <caption>An example comparing the name of persons</caption>
 *
 *  interface Person {
 *     age: number,
 *     name: string
 *  }
 *
 * Observable.of<Person>(
 *     { age: 4, name: 'Foo'},
 *     { age: 7, name: 'Bar'},
 *     { age: 5, name: 'Foo'},
 *     { age: 6, name: 'Foo'})
 *     .distinctUntilKeyChanged('name')
 *     .subscribe(x => console.log(x));
 *
 * // displays:
 * // { age: 4, name: 'Foo' }
 * // { age: 7, name: 'Bar' }
 * // { age: 5, name: 'Foo' }
 *
 * @example <caption>An example comparing the first letters of the name</caption>
 *
 * interface Person {
 *     age: number,
 *     name: string
 *  }
 *
 * Observable.of<Person>(
 *     { age: 4, name: 'Foo1'},
 *     { age: 7, name: 'Bar'},
 *     { age: 5, name: 'Foo2'},
 *     { age: 6, name: 'Foo3'})
 *     .distinctUntilKeyChanged('name', (x: string, y: string) => x.substring(0, 3) === y.substring(0, 3))
 *     .subscribe(x => console.log(x));
 *
 * // displays:
 * // { age: 4, name: 'Foo1' }
 * // { age: 7, name: 'Bar' }
 * // { age: 5, name: 'Foo2' }
 *
 * @see {@link distinct}
 * @see {@link distinctUntilChanged}
 *
 * @param {string} key String key for object property lookup on each item.
 * @param {function} [compare] Optional comparison function called to test if an item is distinct from the previous item in the source.
 * @return {Observable} An Observable that emits items from the source Observable with distinct values based on the key specified.
 * @method distinctUntilKeyChanged
 * @owner Observable
 */
// tslint:disable-next-line:max-line-length
export function distinctUntilKeyChanged<T, K extends keyof T>(this: Observable<T>, key: K, compare?: (x: T[K], y: T[K]) => boolean): Observable<T> {
  return higherOrder<T, K>(key, compare)(this);
}