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import { Observable } from '../Observable';
import { OperatorFunction } from '../types';
/**
* 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
* ```javascript
* import { fromEvent } from 'rxjs';
* import { findIndex } from 'rxjs/operators';
*
* const clicks = fromEvent(document, 'click');
* const result = clicks.pipe(findIndex(ev => ev.target.tagName === 'DIV'));
* result.subscribe(x => console.log(x));
* ```
*
* @see {@link filter}
* @see {@link find}
* @see {@link first}
* @see {@link take}
*
* @param {function(value: T, index: number, source: Observable<T>): boolean} predicate
* A function called with each item to test for condition matching.
* @param {any} [thisArg] An optional argument to determine the value of `this`
* in the `predicate` function.
* @return {Observable} An Observable of the index of the first item that
* matches the condition.
* @method find
* @owner Observable
*/
export declare function findIndex<T>(predicate: (value: T, index: number, source: Observable<T>) => boolean, thisArg?: any): OperatorFunction<T, number>;
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