@reactivex/rxjs/dist/amd/src/add/operator/findIndex.ts

Reactive Extensions for modern JavaScript

import {Observable} from '../../Observable';
import {findIndex, FindIndexSignature} from '../../operator/findIndex';

Observable.prototype.findIndex = findIndex;

declare module '../../Observable' {
  interface Observable<T> {
    findIndex: FindIndexSignature<T>;
  }
}