import { Subscriber } from '../Subscriber'; import { ArgumentOutOfRangeError } from '../util/ArgumentOutOfRangeError'; /** * Emits the single value at the specified `index` in a sequence of emissions * from the source Observable. * * Emits only the i-th value, then completes. * * * * `elementAt` returns an Observable that emits the item at the specified * `index` in the source Observable, or a default value if that `index` is out * of range and the `default` argument is provided. If the `default` argument is * not given and the `index` is out of range, the output Observable will emit an * `ArgumentOutOfRangeError` error. * * @example Emit only the third click event * var clicks = Rx.Observable.fromEvent(document, 'click'); * var result = clicks.elementAt(2); * result.subscribe(x => console.log(x)); * * // Results in: * // click 1 = nothing * // click 2 = nothing * // click 3 = MouseEvent object logged to console * * @see {@link first} * @see {@link last} * @see {@link skip} * @see {@link single} * @see {@link take} * * @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 Is the number `i` for the i-th source emission that has * happened since the subscription, starting from the number `0`. * @param {T} [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. If not, then emits an error. * @method elementAt * @owner Observable */ export function elementAt(index, defaultValue) { return (source) => source.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(); } } //# sourceMappingURL=elementAt.js.map