[6a3a178] | 1 | import { Operator } from '../Operator';
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| 2 | import { Subscriber } from '../Subscriber';
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| 3 | import { ArgumentOutOfRangeError } from '../util/ArgumentOutOfRangeError';
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| 4 | import { Observable } from '../Observable';
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| 5 | import { MonoTypeOperatorFunction, TeardownLogic } from '../types';
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| 6 | import { filter } from './filter';
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| 7 | import { throwIfEmpty } from './throwIfEmpty';
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| 8 | import { defaultIfEmpty } from './defaultIfEmpty';
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| 9 | import { take } from './take';
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| 10 |
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| 11 | /**
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| 12 | * Emits the single value at the specified `index` in a sequence of emissions
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| 13 | * from the source Observable.
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| 14 | *
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| 15 | * <span class="informal">Emits only the i-th value, then completes.</span>
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| 16 | *
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| 17 | * ![](elementAt.png)
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| 18 | *
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| 19 | * `elementAt` returns an Observable that emits the item at the specified
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| 20 | * `index` in the source Observable, or a default value if that `index` is out
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| 21 | * of range and the `default` argument is provided. If the `default` argument is
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| 22 | * not given and the `index` is out of range, the output Observable will emit an
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| 23 | * `ArgumentOutOfRangeError` error.
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| 24 | *
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| 25 | * ## Example
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| 26 | * Emit only the third click event
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| 27 | * ```ts
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| 28 | * import { fromEvent } from 'rxjs';
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| 29 | * import { elementAt } from 'rxjs/operators';
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| 30 | *
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| 31 | * const clicks = fromEvent(document, 'click');
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| 32 | * const result = clicks.pipe(elementAt(2));
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| 33 | * result.subscribe(x => console.log(x));
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| 34 | *
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| 35 | * // Results in:
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| 36 | * // click 1 = nothing
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| 37 | * // click 2 = nothing
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| 38 | * // click 3 = MouseEvent object logged to console
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| 39 | * ```
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| 40 | *
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| 41 | * @see {@link first}
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| 42 | * @see {@link last}
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| 43 | * @see {@link skip}
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| 44 | * @see {@link single}
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| 45 | * @see {@link take}
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| 46 | *
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| 47 | * @throws {ArgumentOutOfRangeError} When using `elementAt(i)`, it delivers an
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| 48 | * ArgumentOutOrRangeError to the Observer's `error` callback if `i < 0` or the
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| 49 | * Observable has completed before emitting the i-th `next` notification.
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| 50 | *
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| 51 | * @param {number} index Is the number `i` for the i-th source emission that has
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| 52 | * happened since the subscription, starting from the number `0`.
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| 53 | * @param {T} [defaultValue] The default value returned for missing indices.
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| 54 | * @return {Observable} An Observable that emits a single item, if it is found.
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| 55 | * Otherwise, will emit the default value if given. If not, then emits an error.
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| 56 | * @method elementAt
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| 57 | * @owner Observable
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| 58 | */
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| 59 | export function elementAt<T>(index: number, defaultValue?: T): MonoTypeOperatorFunction<T> {
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| 60 | if (index < 0) { throw new ArgumentOutOfRangeError(); }
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| 61 | const hasDefaultValue = arguments.length >= 2;
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| 62 | return (source: Observable<T>) => source.pipe(
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| 63 | filter((v, i) => i === index),
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| 64 | take(1),
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| 65 | hasDefaultValue
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| 66 | ? defaultIfEmpty(defaultValue)
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| 67 | : throwIfEmpty(() => new ArgumentOutOfRangeError()),
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| 68 | );
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| 69 | }
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