45 lines
1.8 KiB
TypeScript
45 lines
1.8 KiB
TypeScript
import { Observable } from '../Observable';
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/**
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* Emits the single value at the specified `index` in a sequence of emissions
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* from the source Observable.
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*
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* <span class="informal">Emits only the i-th value, then completes.</span>
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*
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* <img src="./img/elementAt.png" width="100%">
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*
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* `elementAt` returns an Observable that emits the item at the specified
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* `index` in the source Observable, or a default value if that `index` is out
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* of range and the `default` argument is provided. If the `default` argument is
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* not given and the `index` is out of range, the output Observable will emit an
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* `ArgumentOutOfRangeError` error.
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*
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* @example <caption>Emit only the third click event</caption>
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* var clicks = Rx.Observable.fromEvent(document, 'click');
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* var result = clicks.elementAt(2);
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* result.subscribe(x => console.log(x));
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*
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* // Results in:
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* // click 1 = nothing
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* // click 2 = nothing
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* // click 3 = MouseEvent object logged to console
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*
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* @see {@link first}
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* @see {@link last}
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* @see {@link skip}
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* @see {@link single}
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* @see {@link take}
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*
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* @throws {ArgumentOutOfRangeError} When using `elementAt(i)`, it delivers an
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* ArgumentOutOrRangeError to the Observer's `error` callback if `i < 0` or the
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* Observable has completed before emitting the i-th `next` notification.
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*
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* @param {number} index Is the number `i` for the i-th source emission that has
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* happened since the subscription, starting from the number `0`.
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* @param {T} [defaultValue] The default value returned for missing indices.
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* @return {Observable} An Observable that emits a single item, if it is found.
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* Otherwise, will emit the default value if given. If not, then emits an error.
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* @method elementAt
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* @owner Observable
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*/
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export declare function elementAt<T>(this: Observable<T>, index: number, defaultValue?: T): Observable<T>;
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