@reactivex/rxjs
Version:
Reactive Extensions for modern JavaScript
60 lines • 2.19 kB
JavaScript
import { Subscriber } from '../Subscriber';
import { ArgumentOutOfRangeError } from '../util/ArgumentOutOfRangeError';
/**
* Returns an Observable that emits the item at the specified index in the source Observable.
* If default is given, missing indices will output this value on next; otherwise, outputs error.
* @throws {ArgumentOutOfRangeError} When using `elementAt(i)`, it delivers an
* ArgumentOutOrRangeError to the Observer's `error` callback if `i < 0` or the
* Observable has completed before emitting the i-th `next` notification.
* @param {number} index the index of the value to be retrieved.
* @param {any} [defaultValue] the default value returned for missing indices.
* @return {Observable} an Observable that emits a single item, if it is found. Otherwise, will emit the default value if given.
* @method elementAt
* @owner Observable
*/
export function elementAt(index, defaultValue) {
return this.lift(new ElementAtOperator(index, defaultValue));
}
class ElementAtOperator {
constructor(index, defaultValue) {
this.index = index;
this.defaultValue = defaultValue;
if (index < 0) {
throw new ArgumentOutOfRangeError;
}
}
call(subscriber, source) {
return source._subscribe(new ElementAtSubscriber(subscriber, this.index, this.defaultValue));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class ElementAtSubscriber extends Subscriber {
constructor(destination, index, defaultValue) {
super(destination);
this.index = index;
this.defaultValue = defaultValue;
}
_next(x) {
if (this.index-- === 0) {
this.destination.next(x);
this.destination.complete();
}
}
_complete() {
const destination = this.destination;
if (this.index >= 0) {
if (typeof this.defaultValue !== 'undefined') {
destination.next(this.defaultValue);
}
else {
destination.error(new ArgumentOutOfRangeError);
}
}
destination.complete();
}
}
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