fix(#15): improve typing of useObservable

src/use-observable.ts

@@ -1,20 +1,30 @@
 import { Observable, BehaviorSubject } from 'rxjs'
 import { useState, useEffect, useMemo } from 'react'
 
-export type InputFactory<T, U = undefined> = U extends undefined
- ? (state$: Observable<T>) => Observable<T>
- : (inputs$: Observable<U>, state$: Observable<T>) => Observable<T>
+export type InputFactory<State, Inputs = undefined> = Inputs extends undefined
+ ? (state$: Observable<State>) => Observable<State>
+ : (inputs$: Observable<RestrictArray<Inputs>>, state$: Observable<State>) => Observable<State>
 
-export function useObservable<T>(inputFactory: InputFactory<T>): T | null
-export function useObservable<T>(inputFactory: InputFactory<T>, initialState: T): T
-export function useObservable<T, U>(inputFactory: InputFactory<T, U>, initialState: T, inputs: U): T
+export type RestrictArray<T> = T extends any[] ? T : []
 
-export function useObservable<T, U>(inputFactory: InputFactory<T, U>, initialState?: T, inputs?: U): T | null {
+export function useObservable<State>(inputFactory: InputFactory<State>): State | null
+export function useObservable<State>(inputFactory: InputFactory<State>, initialState: State): State
+export function useObservable<State, Inputs>(
+ inputFactory: InputFactory<State, Inputs>,
+ initialState: State,
+ inputs: RestrictArray<Inputs>,
+): State
+
+export function useObservable<State, Inputs extends ReadonlyArray<any>>(
+ inputFactory: InputFactory<State, Inputs>,
+ initialState?: State,
+ inputs?: RestrictArray<Inputs>,
+): State | null {
  const [state, setState] = useState(typeof initialState !== 'undefined' ? initialState : null)
 
  const { state$, inputs$ } = useMemo(() => {
- const stateSubject$ = new BehaviorSubject<T | undefined>(initialState)
- const inputSubject$ = new BehaviorSubject<U | undefined>(inputs)
+ const stateSubject$ = new BehaviorSubject<State | undefined>(initialState)
+ const inputSubject$ = new BehaviorSubject<RestrictArray<Inputs> | undefined>(inputs)
 
  return {
  state$: stateSubject$,
@@ -24,18 +34,20 @@ export function useObservable<T, U>(inputFactory: InputFactory<T, U>, initialSta
 
  useMemo(() => {
  inputs$.next(inputs)
- }, ((inputs as unknown) as ReadonlyArray<any>) || [])
+ }, inputs || [])
 
  useEffect(
  () => {
- let output$: BehaviorSubject<T>
+ let output$: BehaviorSubject<State>
  if (inputs) {
  output$ = (inputFactory as (
- inputs$: Observable<U | undefined>,
- state$: Observable<T | undefined>,
- ) => Observable<T>)(inputs$, state$) as BehaviorSubject<T>
+ inputs$: Observable<RestrictArray<Inputs> | undefined>,
+ state$: Observable<State | undefined>,
+ ) => Observable<State>)(inputs$, state$) as BehaviorSubject<State>
  } else {
- output$ = (inputFactory as (state$: Observable<T | undefined>) => Observable<T>)(state$) as BehaviorSubject<T>
+ output$ = (inputFactory as (state$: Observable<State | undefined>) => Observable<State>)(
+ state$,
+ ) as BehaviorSubject<State>
  }
  const subscription = output$.subscribe((value) => {
  state$.next(value)