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

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2019-12-02 12:22:45 +00:00
import { Subscriber } from '../Subscriber';
import { EmptyError } from '../util/EmptyError';
/**
* Returns an Observable that emits the single item emitted by the source Observable that matches a specified
* predicate, if that Observable emits one such item. If the source Observable emits more than one such item or no
* such items, notify of an IllegalArgumentException or NoSuchElementException respectively.
*
* <img src="./img/single.png" width="100%">
*
* @throws {EmptyError} Delivers an EmptyError to the Observer's `error`
* callback if the Observable completes before any `next` notification was sent.
* @param {Function} predicate - A predicate function to evaluate items emitted by the source Observable.
* @return {Observable<T>} An Observable that emits the single item emitted by the source Observable that matches
* the predicate.
.
* @method single
* @owner Observable
*/
export function single(predicate) {
return (source) => source.lift(new SingleOperator(predicate, source));
}
class SingleOperator {
constructor(predicate, source) {
this.predicate = predicate;
this.source = source;
}
call(subscriber, source) {
return source.subscribe(new SingleSubscriber(subscriber, this.predicate, this.source));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class SingleSubscriber extends Subscriber {
constructor(destination, predicate, source) {
super(destination);
this.predicate = predicate;
this.source = source;
this.seenValue = false;
this.index = 0;
}
applySingleValue(value) {
if (this.seenValue) {
this.destination.error('Sequence contains more than one element');
}
else {
this.seenValue = true;
this.singleValue = value;
}
}
_next(value) {
const index = this.index++;
if (this.predicate) {
this.tryNext(value, index);
}
else {
this.applySingleValue(value);
}
}
tryNext(value, index) {
try {
if (this.predicate(value, index, this.source)) {
this.applySingleValue(value);
}
}
catch (err) {
this.destination.error(err);
}
}
_complete() {
const destination = this.destination;
if (this.index > 0) {
destination.next(this.seenValue ? this.singleValue : undefined);
destination.complete();
}
else {
destination.error(new EmptyError);
}
}
}
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