| import { Operator } from '../Operator'; |
| import { Subscriber } from '../Subscriber'; |
| import { ArgumentOutOfRangeError } from '../util/ArgumentOutOfRangeError'; |
| import { empty } from '../observable/empty'; |
| import { Observable } from '../Observable'; |
| import { MonoTypeOperatorFunction, TeardownLogic } from '../types'; |
| |
| /** |
| * Emits only the last `count` values emitted by the source Observable. |
| * |
| * <span class="informal">Remembers the latest `count` values, then emits those |
| * only when the source completes.</span> |
| * |
| * ![](takeLast.png) |
| * |
| * `takeLast` returns an Observable that emits at most the last `count` values |
| * emitted by the source Observable. If the source emits fewer than `count` |
| * values then all of its values are emitted. This operator must wait until the |
| * `complete` notification emission from the source in order to emit the `next` |
| * values on the output Observable, because otherwise it is impossible to know |
| * whether or not more values will be emitted on the source. For this reason, |
| * all values are emitted synchronously, followed by the complete notification. |
| * |
| * ## Example |
| * Take the last 3 values of an Observable with many values |
| * ```ts |
| * import { range } from 'rxjs'; |
| * import { takeLast } from 'rxjs/operators'; |
| * |
| * const many = range(1, 100); |
| * const lastThree = many.pipe(takeLast(3)); |
| * lastThree.subscribe(x => console.log(x)); |
| * ``` |
| * |
| * @see {@link take} |
| * @see {@link takeUntil} |
| * @see {@link takeWhile} |
| * @see {@link skip} |
| * |
| * @throws {ArgumentOutOfRangeError} When using `takeLast(i)`, it delivers an |
| * ArgumentOutOrRangeError to the Observer's `error` callback if `i < 0`. |
| * |
| * @param {number} count The maximum number of values to emit from the end of |
| * the sequence of values emitted by the source Observable. |
| * @return {Observable<T>} An Observable that emits at most the last count |
| * values emitted by the source Observable. |
| * @method takeLast |
| * @owner Observable |
| */ |
| export function takeLast<T>(count: number): MonoTypeOperatorFunction<T> { |
| return function takeLastOperatorFunction(source: Observable<T>): Observable<T> { |
| if (count === 0) { |
| return empty(); |
| } else { |
| return source.lift(new TakeLastOperator(count)); |
| } |
| }; |
| } |
| |
| class TakeLastOperator<T> implements Operator<T, T> { |
| constructor(private total: number) { |
| if (this.total < 0) { |
| throw new ArgumentOutOfRangeError; |
| } |
| } |
| |
| call(subscriber: Subscriber<T>, source: any): TeardownLogic { |
| return source.subscribe(new TakeLastSubscriber(subscriber, this.total)); |
| } |
| } |
| |
| /** |
| * We need this JSDoc comment for affecting ESDoc. |
| * @ignore |
| * @extends {Ignored} |
| */ |
| class TakeLastSubscriber<T> extends Subscriber<T> { |
| private ring: Array<T> = new Array(); |
| private count: number = 0; |
| |
| constructor(destination: Subscriber<T>, private total: number) { |
| super(destination); |
| } |
| |
| protected _next(value: T): void { |
| const ring = this.ring; |
| const total = this.total; |
| const count = this.count++; |
| |
| if (ring.length < total) { |
| ring.push(value); |
| } else { |
| const index = count % total; |
| ring[index] = value; |
| } |
| } |
| |
| protected _complete(): void { |
| const destination = this.destination; |
| let count = this.count; |
| |
| if (count > 0) { |
| const total = this.count >= this.total ? this.total : this.count; |
| const ring = this.ring; |
| |
| for (let i = 0; i < total; i++) { |
| const idx = (count++) % total; |
| destination.next(ring[idx]); |
| } |
| } |
| |
| destination.complete(); |
| } |
| } |