work.suroh.tk/node_modules/rxjs/_esm2015/operators/skipLast.js

83 lines
2.6 KiB
JavaScript

import { Subscriber } from '../Subscriber';
import { ArgumentOutOfRangeError } from '../util/ArgumentOutOfRangeError';
/**
* Skip the last `count` values emitted by the source Observable.
*
* <img src="./img/skipLast.png" width="100%">
*
* `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 <caption>Skip the last 2 values of an Observable with many values</caption>
* var many = Rx.Observable.range(1, 5);
* var skipLastTwo = many.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(count) {
return (source) => source.lift(new SkipLastOperator(count));
}
class SkipLastOperator {
constructor(_skipCount) {
this._skipCount = _skipCount;
if (this._skipCount < 0) {
throw new ArgumentOutOfRangeError;
}
}
call(subscriber, source) {
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 extends Subscriber {
constructor(destination, _skipCount) {
super(destination);
this._skipCount = _skipCount;
this._count = 0;
this._ring = new Array(_skipCount);
}
_next(value) {
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);
}
}
}
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