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