@reactivex/rxjs/src/operator/take.ts

Reactive Extensions for modern JavaScript

import {Operator} from '../Operator';
import {Subscriber} from '../Subscriber';
import {ArgumentOutOfRangeError} from '../util/ArgumentOutOfRangeError';
import {EmptyObservable} from '../observable/EmptyObservable';
import {Observable} from '../Observable';

/**
 * 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>
 *
 * <img src="./img/take.png" width="100%">
 *
 * `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 <caption>Take the first 5 seconds of an infinite 1-second interval Observable</caption>
 * var interval = Rx.Observable.interval(1000);
 * var five = interval.take(5);
 * five.subscribe(x => console.log(x));
 *
 * @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): Observable<T> {
  if (count === 0) {
    return new EmptyObservable<T>();
  } else {
    return this.lift(new TakeOperator(count));
  }
}

export interface TakeSignature<T> {
  (count: number): Observable<T>;
}

class TakeOperator<T> implements Operator<T, T> {
  constructor(private total: number) {
    if (this.total < 0) {
      throw new ArgumentOutOfRangeError;
    }
  }

  call(subscriber: Subscriber<T>, source: any): any {
    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;
    if (++this.count <= total) {
      this.destination.next(value);
      if (this.count === total) {
        this.destination.complete();
        this.unsubscribe();
      }
    }
  }
}