| 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 first `count` values emitted by the source Observable. |
| * |
| * <span class="informal">Takes the first `count` values from the source, then |
| * completes.</span> |
| * |
| * ![](take.png) |
| * |
| * `take` returns an Observable that emits only the first `count` values emitted |
| * by the source Observable. If the source emits fewer than `count` values then |
| * all of its values are emitted. After that, it completes, regardless if the |
| * source completes. |
| * |
| * ## Example |
| * Take the first 5 seconds of an infinite 1-second interval Observable |
| * ```ts |
| * import { interval } from 'rxjs'; |
| * import { take } from 'rxjs/operators'; |
| * |
| * const intervalCount = interval(1000); |
| * const takeFive = intervalCount.pipe(take(5)); |
| * takeFive.subscribe(x => console.log(x)); |
| * |
| * // Logs: |
| * // 0 |
| * // 1 |
| * // 2 |
| * // 3 |
| * // 4 |
| * ``` |
| * |
| * @see {@link takeLast} |
| * @see {@link takeUntil} |
| * @see {@link takeWhile} |
| * @see {@link skip} |
| * |
| * @throws {ArgumentOutOfRangeError} When using `take(i)`, it delivers an |
| * ArgumentOutOrRangeError to the Observer's `error` callback if `i < 0`. |
| * |
| * @param {number} count The maximum number of `next` values to emit. |
| * @return {Observable<T>} An Observable that emits only the first `count` |
| * values emitted by the source Observable, or all of the values from the source |
| * if the source emits fewer than `count` values. |
| * @method take |
| * @owner Observable |
| */ |
| export function take<T>(count: number): MonoTypeOperatorFunction<T> { |
| return (source: Observable<T>) => { |
| if (count === 0) { |
| return empty(); |
| } else { |
| return source.lift(new TakeOperator(count)); |
| } |
| }; |
| } |
| |
| class TakeOperator<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 TakeSubscriber(subscriber, this.total)); |
| } |
| } |
| |
| /** |
| * We need this JSDoc comment for affecting ESDoc. |
| * @ignore |
| * @extends {Ignored} |
| */ |
| class TakeSubscriber<T> extends Subscriber<T> { |
| private count: number = 0; |
| |
| constructor(destination: Subscriber<T>, private total: number) { |
| super(destination); |
| } |
| |
| protected _next(value: T): void { |
| const total = this.total; |
| const count = ++this.count; |
| if (count <= total) { |
| this.destination.next(value); |
| if (count === total) { |
| this.destination.complete(); |
| this.unsubscribe(); |
| } |
| } |
| } |
| } |