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feat(last): add higher-order lettable version of last
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,133 @@ | ||
| import { Observable } from '../Observable'; | ||
| import { Operator } from '../Operator'; | ||
| import { Subscriber } from '../Subscriber'; | ||
| import { EmptyError } from '../util/EmptyError'; | ||
| import { OperatorFunction, MonoTypeOperatorFunction } from '../interfaces'; | ||
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| /* tslint:disable:max-line-length */ | ||
| export function last<T, S extends T>(predicate: (value: T, index: number, source: Observable<T>) => value is S): OperatorFunction<T, S>; | ||
| export function last<T, S extends T, R>(predicate: (value: T | S, index: number, source: Observable<T>) => value is S, | ||
| resultSelector: (value: S, index: number) => R, defaultValue?: R): OperatorFunction<T, R>; | ||
| export function last<T, S extends T>(predicate: (value: T, index: number, source: Observable<T>) => value is S, | ||
| resultSelector: void, | ||
| defaultValue?: S): OperatorFunction<T, S>; | ||
| export function last<T>(predicate?: (value: T, index: number, source: Observable<T>) => boolean): MonoTypeOperatorFunction<T>; | ||
| export function last<T, R>(predicate: (value: T, index: number, source: Observable<T>) => boolean, | ||
| resultSelector?: (value: T, index: number) => R, | ||
| defaultValue?: R): OperatorFunction<T, R>; | ||
| export function last<T>(predicate: (value: T, index: number, source: Observable<T>) => boolean, | ||
| resultSelector: void, | ||
| defaultValue?: T): MonoTypeOperatorFunction<T>; | ||
| /* tslint:enable:max-line-length */ | ||
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| /** | ||
| * Returns an Observable that emits only the last item emitted by the source Observable. | ||
| * It optionally takes a predicate function as a parameter, in which case, rather than emitting | ||
| * the last item from the source Observable, the resulting Observable will emit the last item | ||
| * from the source Observable that satisfies the predicate. | ||
| * | ||
| * <img src="./img/last.png" width="100%"> | ||
| * | ||
| * @throws {EmptyError} Delivers an EmptyError to the Observer's `error` | ||
| * callback if the Observable completes before any `next` notification was sent. | ||
| * @param {function} predicate - The condition any source emitted item has to satisfy. | ||
| * @return {Observable} An Observable that emits only the last item satisfying the given condition | ||
| * from the source, or an NoSuchElementException if no such items are emitted. | ||
| * @throws - Throws if no items that match the predicate are emitted by the source Observable. | ||
| * @method last | ||
| * @owner Observable | ||
| */ | ||
| export function last<T, R>(predicate?: (value: T, index: number, source: Observable<T>) => boolean, | ||
| resultSelector?: ((value: T, index: number) => R) | void, | ||
| defaultValue?: R): OperatorFunction<T, T | R> { | ||
| return (source: Observable<T>) => source.lift(new LastOperator(predicate, resultSelector, defaultValue, source)); | ||
| } | ||
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| class LastOperator<T, R> implements Operator<T, R> { | ||
| constructor(private predicate?: (value: T, index: number, source: Observable<T>) => boolean, | ||
| private resultSelector?: ((value: T, index: number) => R) | void, | ||
| private defaultValue?: any, | ||
| private source?: Observable<T>) { | ||
| } | ||
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| call(observer: Subscriber<R>, source: any): any { | ||
| return source.subscribe(new LastSubscriber(observer, this.predicate, this.resultSelector, this.defaultValue, this.source)); | ||
| } | ||
| } | ||
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| /** | ||
| * We need this JSDoc comment for affecting ESDoc. | ||
| * @ignore | ||
| * @extends {Ignored} | ||
| */ | ||
| class LastSubscriber<T, R> extends Subscriber<T> { | ||
| private lastValue: T | R; | ||
| private hasValue: boolean = false; | ||
| private index: number = 0; | ||
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| constructor(destination: Subscriber<R>, | ||
| private predicate?: (value: T, index: number, source: Observable<T>) => boolean, | ||
| private resultSelector?: ((value: T, index: number) => R) | void, | ||
| private defaultValue?: any, | ||
| private source?: Observable<T>) { | ||
| super(destination); | ||
| if (typeof defaultValue !== 'undefined') { | ||
| this.lastValue = defaultValue; | ||
| this.hasValue = true; | ||
| } | ||
| } | ||
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| protected _next(value: T): void { | ||
| const index = this.index++; | ||
| if (this.predicate) { | ||
| this._tryPredicate(value, index); | ||
| } else { | ||
| if (this.resultSelector) { | ||
| this._tryResultSelector(value, index); | ||
| return; | ||
| } | ||
| this.lastValue = value; | ||
| this.hasValue = true; | ||
| } | ||
| } | ||
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| private _tryPredicate(value: T, index: number) { | ||
| let result: any; | ||
| try { | ||
| result = this.predicate(value, index, this.source); | ||
| } catch (err) { | ||
| this.destination.error(err); | ||
| return; | ||
| } | ||
| if (result) { | ||
| if (this.resultSelector) { | ||
| this._tryResultSelector(value, index); | ||
| return; | ||
| } | ||
| this.lastValue = value; | ||
| this.hasValue = true; | ||
| } | ||
| } | ||
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| private _tryResultSelector(value: T, index: number) { | ||
| let result: any; | ||
| try { | ||
| result = (<any>this).resultSelector(value, index); | ||
| } catch (err) { | ||
| this.destination.error(err); | ||
| return; | ||
| } | ||
| this.lastValue = result; | ||
| this.hasValue = true; | ||
| } | ||
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| protected _complete(): void { | ||
| const destination = this.destination; | ||
| if (this.hasValue) { | ||
| destination.next(this.lastValue); | ||
| destination.complete(); | ||
| } else { | ||
| destination.error(new EmptyError); | ||
| } | ||
| } | ||
| } |