update

node_modules/rxjs/operators/findIndex.d.ts

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+import { Observable } from '../Observable';
+import { OperatorFunction } from '../interfaces';
+/**
+ * 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>
+ *
+ * <img src="./img/findIndex.png" width="100%">
+ *
+ * `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 <caption>Emit the index of first click that happens on a DIV element</caption>
+ * var clicks = Rx.Observable.fromEvent(document, 'click');
+ * var result = clicks.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>;