| import { Operator } from '../Operator'; |
| import { Subscriber } from '../Subscriber'; |
| import { Observable } from '../Observable'; |
| import { OperatorFunction } from '../types'; |
| |
| /** |
| * Emits the given constant value on the output Observable every time the source |
| * Observable emits a value. |
| * |
| * <span class="informal">Like {@link map}, but it maps every source value to |
| * the same output value every time.</span> |
| * |
| * ![](mapTo.png) |
| * |
| * Takes a constant `value` as argument, and emits that whenever the source |
| * Observable emits a value. In other words, ignores the actual source value, |
| * and simply uses the emission moment to know when to emit the given `value`. |
| * |
| * ## Example |
| * Map every click to the string 'Hi' |
| * ```ts |
| * import { fromEvent } from 'rxjs'; |
| * import { mapTo } from 'rxjs/operators'; |
| * |
| * const clicks = fromEvent(document, 'click'); |
| * const greetings = clicks.pipe(mapTo('Hi')); |
| * greetings.subscribe(x => console.log(x)); |
| * ``` |
| * |
| * @see {@link map} |
| * |
| * @param {any} value The value to map each source value to. |
| * @return {Observable} An Observable that emits the given `value` every time |
| * the source Observable emits something. |
| * @method mapTo |
| * @owner Observable |
| */ |
| export function mapTo<T, R>(value: R): OperatorFunction<T, R> { |
| return (source: Observable<T>) => source.lift(new MapToOperator(value)); |
| } |
| |
| class MapToOperator<T, R> implements Operator<T, R> { |
| |
| value: R; |
| |
| constructor(value: R) { |
| this.value = value; |
| } |
| |
| call(subscriber: Subscriber<R>, source: any): any { |
| return source.subscribe(new MapToSubscriber(subscriber, this.value)); |
| } |
| } |
| |
| /** |
| * We need this JSDoc comment for affecting ESDoc. |
| * @ignore |
| * @extends {Ignored} |
| */ |
| class MapToSubscriber<T, R> extends Subscriber<T> { |
| |
| value: R; |
| |
| constructor(destination: Subscriber<R>, value: R) { |
| super(destination); |
| this.value = value; |
| } |
| |
| protected _next(x: T) { |
| this.destination.next(this.value); |
| } |
| } |