| import { distinctUntilChanged } from './distinctUntilChanged'; |
| import { MonoTypeOperatorFunction } from '../types'; |
| |
| /* tslint:disable:max-line-length */ |
| export function distinctUntilKeyChanged<T>(key: keyof T): MonoTypeOperatorFunction<T>; |
| export function distinctUntilKeyChanged<T, K extends keyof T>(key: K, compare: (x: T[K], y: T[K]) => boolean): MonoTypeOperatorFunction<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. |
| * |
| * ## Examples |
| * An example comparing the name of persons |
| * ```typescript |
| * import { of } from 'rxjs'; |
| * import { distinctUntilKeyChanged } from 'rxjs/operators'; |
| * |
| * interface Person { |
| * age: number, |
| * name: string |
| * } |
| * |
| * of<Person>( |
| * { 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' } |
| * ``` |
| * |
| * An example comparing the first letters of the name |
| * ```typescript |
| * import { of } from 'rxjs'; |
| * import { distinctUntilKeyChanged } from 'rxjs/operators'; |
| * |
| * interface Person { |
| * age: number, |
| * name: string |
| * } |
| * |
| * of<Person>( |
| * { age: 4, name: 'Foo1'}, |
| * { age: 7, name: 'Bar'}, |
| * { age: 5, name: 'Foo2'}, |
| * { age: 6, name: 'Foo3'}, |
| * ).pipe( |
| * 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 |
| */ |
| export function distinctUntilKeyChanged<T, K extends keyof T>(key: K, compare?: (x: T[K], y: T[K]) => boolean): MonoTypeOperatorFunction<T> { |
| return distinctUntilChanged((x: T, y: T) => compare ? compare(x[key], y[key]) : x[key] === y[key]); |
| } |