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49 lines
1.9 KiB
49 lines
1.9 KiB
import { Observable } from '../Observable'; |
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import { MonoTypeOperatorFunction } from '../types'; |
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/** |
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* Returns an Observable that emits the single item emitted by the source Observable that matches a specified |
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* predicate, if that Observable emits one such item. If the source Observable emits more than one such item or no |
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* items, notify of an IllegalArgumentException or NoSuchElementException respectively. If the source Observable |
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* emits items but none match the specified predicate then `undefined` is emitted. |
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* |
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* <span class="informal">Like {@link first}, but emit with error notification if there is more than one value.</span> |
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*  |
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* |
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* ## Example |
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* emits 'error' |
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* ```ts |
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* import { range } from 'rxjs'; |
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* import { single } from 'rxjs/operators'; |
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* |
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* const numbers = range(1,5).pipe(single()); |
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* numbers.subscribe(x => console.log('never get called'), e => console.log('error')); |
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* // result |
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* // 'error' |
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* ``` |
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* |
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* emits 'undefined' |
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* ```ts |
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* import { range } from 'rxjs'; |
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* import { single } from 'rxjs/operators'; |
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* |
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* const numbers = range(1,5).pipe(single(x => x === 10)); |
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* numbers.subscribe(x => console.log(x)); |
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* // result |
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* // 'undefined' |
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* ``` |
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* |
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* @see {@link first} |
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* @see {@link find} |
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* @see {@link findIndex} |
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* @see {@link elementAt} |
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* |
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* @throws {EmptyError} Delivers an EmptyError to the Observer's `error` |
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* callback if the Observable completes before any `next` notification was sent. |
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* @param {Function} predicate - A predicate function to evaluate items emitted by the source Observable. |
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* @return {Observable<T>} An Observable that emits the single item emitted by the source Observable that matches |
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* the predicate or `undefined` when no items match. |
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* |
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* @method single |
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* @owner Observable |
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*/ |
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export declare function single<T>(predicate?: (value: T, index: number, source: Observable<T>) => boolean): MonoTypeOperatorFunction<T>;
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