83 lines
2.6 KiB
JavaScript
83 lines
2.6 KiB
JavaScript
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import { Subscriber } from '../Subscriber';
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import { EmptyError } from '../util/EmptyError';
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/**
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* Returns an Observable that emits the single item emitted by the source Observable that matches a specified
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* predicate, if that Observable emits one such item. If the source Observable emits more than one such item or no
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* such items, notify of an IllegalArgumentException or NoSuchElementException respectively.
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*
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* <img src="./img/single.png" width="100%">
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*
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* @throws {EmptyError} Delivers an EmptyError to the Observer's `error`
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* callback if the Observable completes before any `next` notification was sent.
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* @param {Function} predicate - A predicate function to evaluate items emitted by the source Observable.
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* @return {Observable<T>} An Observable that emits the single item emitted by the source Observable that matches
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* the predicate.
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.
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* @method single
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* @owner Observable
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*/
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export function single(predicate) {
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return (source) => source.lift(new SingleOperator(predicate, source));
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}
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class SingleOperator {
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constructor(predicate, source) {
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this.predicate = predicate;
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this.source = source;
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}
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call(subscriber, source) {
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return source.subscribe(new SingleSubscriber(subscriber, this.predicate, this.source));
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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 SingleSubscriber extends Subscriber {
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constructor(destination, predicate, source) {
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super(destination);
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this.predicate = predicate;
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this.source = source;
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this.seenValue = false;
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this.index = 0;
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}
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applySingleValue(value) {
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if (this.seenValue) {
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this.destination.error('Sequence contains more than one element');
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}
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else {
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this.seenValue = true;
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this.singleValue = value;
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}
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}
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_next(value) {
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const index = this.index++;
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if (this.predicate) {
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this.tryNext(value, index);
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}
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else {
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this.applySingleValue(value);
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}
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}
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tryNext(value, index) {
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try {
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if (this.predicate(value, index, this.source)) {
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this.applySingleValue(value);
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}
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}
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catch (err) {
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this.destination.error(err);
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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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if (this.index > 0) {
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destination.next(this.seenValue ? this.singleValue : undefined);
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destination.complete();
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}
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else {
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destination.error(new EmptyError);
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}
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}
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}
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//# sourceMappingURL=single.js.map
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