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43 lines
1.7 KiB
43 lines
1.7 KiB
import { Observable } from '../Observable'; |
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import { OperatorFunction } from '../types'; |
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/** |
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* Emits only the index of the first value emitted by the source Observable that |
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* meets some condition. |
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* |
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* <span class="informal">It's like {@link find}, but emits the index of the |
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* found value, not the value itself.</span> |
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* |
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*  |
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* |
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* `findIndex` searches for the first item in the source Observable that matches |
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* the specified condition embodied by the `predicate`, and returns the |
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* (zero-based) index of the first occurrence in the source. Unlike |
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* {@link first}, the `predicate` is required in `findIndex`, and does not emit |
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* an error if a valid value is not found. |
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* |
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* ## Example |
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* Emit the index of first click that happens on a DIV element |
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* ```ts |
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* import { fromEvent } from 'rxjs'; |
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* import { findIndex } from 'rxjs/operators'; |
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* |
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* const clicks = fromEvent(document, 'click'); |
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* const result = clicks.pipe(findIndex(ev => ev.target.tagName === 'DIV')); |
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* result.subscribe(x => console.log(x)); |
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* ``` |
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* |
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* @see {@link filter} |
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* @see {@link find} |
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* @see {@link first} |
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* @see {@link take} |
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* |
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* @param {function(value: T, index: number, source: Observable<T>): boolean} predicate |
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* A function called with each item to test for condition matching. |
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* @param {any} [thisArg] An optional argument to determine the value of `this` |
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* in the `predicate` function. |
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* @return {Observable} An Observable of the index of the first item that |
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* matches the condition. |
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* @method find |
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* @owner Observable |
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*/ |
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export declare function findIndex<T>(predicate: (value: T, index: number, source: Observable<T>) => boolean, thisArg?: any): OperatorFunction<T, number>;
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