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import { Observable } from '../Observable';
import { Falsy, OperatorFunction } from '../types';
import { operate } from '../util/lift';
import { createFind } from './find';
export function findIndex<T>(predicate: BooleanConstructor): OperatorFunction<T, T extends Falsy ? -1 : number>;
/** @deprecated Use a closure instead of a `thisArg`. Signatures accepting a `thisArg` will be removed in v8. */
export function findIndex<T>(predicate: BooleanConstructor, thisArg: any): OperatorFunction<T, T extends Falsy ? -1 : number>;
/** @deprecated Use a closure instead of a `thisArg`. Signatures accepting a `thisArg` will be removed in v8. */
export function findIndex<T, A>(
predicate: (this: A, value: T, index: number, source: Observable<T>) => boolean,
thisArg: A
): OperatorFunction<T, number>;
export function findIndex<T>(predicate: (value: T, index: number, source: Observable<T>) => boolean): OperatorFunction<T, number>;
/**
* Emits only the index of the first value emitted by the source Observable that
* meets some condition.
*
* <span class="informal">It's like {@link find}, but emits the index of the
* found value, not the value itself.</span>
*
* 
*
* `findIndex` searches for the first item in the source Observable that matches
* the specified condition embodied by the `predicate`, and returns the
* (zero-based) index of the first occurrence in the source. Unlike
* {@link first}, the `predicate` is required in `findIndex`, and does not emit
* an error if a valid value is not found.
*
* ## Example
*
* Emit the index of first click that happens on a DIV element
*
* ```ts
* import { fromEvent, findIndex } from 'rxjs';
*
* const div = document.createElement('div');
* div.style.cssText = 'width: 200px; height: 200px; background: #09c;';
* document.body.appendChild(div);
*
* const clicks = fromEvent(document, 'click');
* const result = clicks.pipe(findIndex(ev => (<HTMLElement>ev.target).tagName === 'DIV'));
* result.subscribe(x => console.log(x));
* ```
*
* @see {@link filter}
* @see {@link find}
* @see {@link first}
* @see {@link take}
*
* @param predicate A function called with each item to test for condition matching.
* @param thisArg An optional argument to determine the value of `this` in the
* `predicate` function.
* @return A function that returns an Observable that emits the index of the
* first item that matches the condition.
*/
export function findIndex<T>(
predicate: (value: T, index: number, source: Observable<T>) => boolean,
thisArg?: any
): OperatorFunction<T, number> {
return operate(createFind(predicate, thisArg, 'index'));
}
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