import {Operator} from '../Operator';
import {Subscriber} from '../Subscriber';
import {ArgumentOutOfRangeError} from '../util/ArgumentOutOfRangeError';
import {Observable} from '../Observable';
/**
* 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.
* @param {number} index the index of the value to be retrieved.
* @param {any} [defaultValue] the default value returned for missing indices.
* @returns {Observable} an Observable that emits a single item, if it is found. Otherwise, will emit the default value if given.
*/
export function elementAt<T>(index: number, defaultValue?: T): Observable<T> {
return this.lift(new ElementAtOperator(index, defaultValue));
}
class ElementAtOperator<T> implements Operator<T, T> {
constructor(private index: number, private defaultValue?: T) {
if (index < 0) {
throw new ArgumentOutOfRangeError;
}
}
call(subscriber: Subscriber<T>): Subscriber<T> {
return new ElementAtSubscriber(subscriber, this.index, this.defaultValue);
}
}
class ElementAtSubscriber<T> extends Subscriber<T> {
constructor(destination: Subscriber<T>, private index: number, private defaultValue?: T) {
super(destination);
}
protected _next(x: T) {
if (this.index-- === 0) {
this.destination.next(x);
this.destination.complete();
}
}
protected _complete() {
const destination = this.destination;
Eif (this.index >= 0) {
if (typeof this.defaultValue !== 'undefined') {
destination.next(this.defaultValue);
} else {
destination.error(new ArgumentOutOfRangeError);
}
}
destination.complete();
}
}
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