typed rxjs/operator/pluck

getin.ts

import { Observable } from 'rxjs/Observable'
import { of } from 'rxjs/observable/of'
import { map } from 'rxjs/operators'

/**
 * Typesafe rxjs/operators/plunk
 * @example
 * const state$ = of({ counter: { count: 0 } })
 * state$.pipe(getIn('counter', 'count')) //-> Observable<number>
 */
export function getIn<K extends string>(k: K)
    : <T extends {[P in K]?: T[P]}>(src$: Observable<T>) => Observable<T[K]>
export function getIn<K1 extends string, K2 extends string>(k: K1, k2: K2)
    : <T extends {[P1 in K1]: {[P2 in K2]: T[P1][P2]}}>(src$: Observable<T>) => Observable<T[K1][K2]>
export function getIn<K1 extends string, K2 extends string, K3 extends string>(k: K1, k2: K2, K3: K3)
    : <T extends {[P1 in K1]: {[P2 in K2]: {[P3 in K3]: T[P1][P2][P3]}}}>(src$: Observable<T>) => Observable<T[K1][K2][K3]>
export function getIn(...path: string[]) {
    return (src$: Observable<any>) => {
        try {
            return src$.pipe(map((src: any) => path.reduce((acc, k) => acc[k], src)))
        } catch (e) {
            return of(undefined)
        }
    }
}