| import { Operator } from '../Operator'; |
| import { Subscriber } from '../Subscriber'; |
| import { ArgumentOutOfRangeError } from '../util/ArgumentOutOfRangeError'; |
| import { Observable } from '../Observable'; |
| import { MonoTypeOperatorFunction, TeardownLogic } from '../types'; |
| |
| /** |
| * Skip the last `count` values emitted by the source Observable. |
| * |
| * ![](skipLast.png) |
| * |
| * `skipLast` returns an Observable that accumulates a queue with a length |
| * enough to store the first `count` values. As more values are received, |
| * values are taken from the front of the queue and produced on the result |
| * sequence. This causes values to be delayed. |
| * |
| * ## Example |
| * Skip the last 2 values of an Observable with many values |
| * ```ts |
| * import { range } from 'rxjs'; |
| * import { skipLast } from 'rxjs/operators'; |
| * |
| * const many = range(1, 5); |
| * const skipLastTwo = many.pipe(skipLast(2)); |
| * skipLastTwo.subscribe(x => console.log(x)); |
| * |
| * // Results in: |
| * // 1 2 3 |
| * ``` |
| * |
| * @see {@link skip} |
| * @see {@link skipUntil} |
| * @see {@link skipWhile} |
| * @see {@link take} |
| * |
| * @throws {ArgumentOutOfRangeError} When using `skipLast(i)`, it throws |
| * ArgumentOutOrRangeError if `i < 0`. |
| * |
| * @param {number} count Number of elements to skip from the end of the source Observable. |
| * @returns {Observable<T>} An Observable that skips the last count values |
| * emitted by the source Observable. |
| * @method skipLast |
| * @owner Observable |
| */ |
| export function skipLast<T>(count: number): MonoTypeOperatorFunction<T> { |
| return (source: Observable<T>) => source.lift(new SkipLastOperator(count)); |
| } |
| |
| class SkipLastOperator<T> implements Operator<T, T> { |
| constructor(private _skipCount: number) { |
| if (this._skipCount < 0) { |
| throw new ArgumentOutOfRangeError; |
| } |
| } |
| |
| call(subscriber: Subscriber<T>, source: any): TeardownLogic { |
| if (this._skipCount === 0) { |
| // If we don't want to skip any values then just subscribe |
| // to Subscriber without any further logic. |
| return source.subscribe(new Subscriber(subscriber)); |
| } else { |
| return source.subscribe(new SkipLastSubscriber(subscriber, this._skipCount)); |
| } |
| } |
| } |
| |
| /** |
| * We need this JSDoc comment for affecting ESDoc. |
| * @ignore |
| * @extends {Ignored} |
| */ |
| class SkipLastSubscriber<T> extends Subscriber<T> { |
| private _ring: T[]; |
| private _count: number = 0; |
| |
| constructor(destination: Subscriber<T>, private _skipCount: number) { |
| super(destination); |
| this._ring = new Array<T>(_skipCount); |
| } |
| |
| protected _next(value: T): void { |
| const skipCount = this._skipCount; |
| const count = this._count++; |
| |
| if (count < skipCount) { |
| this._ring[count] = value; |
| } else { |
| const currentIndex = count % skipCount; |
| const ring = this._ring; |
| const oldValue = ring[currentIndex]; |
| |
| ring[currentIndex] = value; |
| this.destination.next(oldValue); |
| } |
| } |
| } |