import { Observable } from '../Observable'; import { FindValueOperator } from '../operators/find'; 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 * ```ts * 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 function findIndex<T>(predicate: (value: T, index: number, source: Observable<T>) => boolean, thisArg?: any): OperatorFunction<T, number> { return (source: Observable<T>) => source.lift(new FindValueOperator(predicate, source, true, thisArg)) as Observable<any>; }