From 25f8eec4484f5ffdf85fb45cf65d5fa7d96fcf57 Mon Sep 17 00:00:00 2001
From: crimx <straybugs@gmail.com>
Date: Fri, 15 Oct 2021 18:10:56 +0800
Subject: [PATCH] feat(observable-hooks): better type infer for BehaviorSubject

---
 .../__tests__/use-observable-state.spec.ts    | 16 +++++++++++++-
 .../src/use-observable-state.ts               | 21 +++++++------------
 2 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/packages/observable-hooks/__tests__/use-observable-state.spec.ts b/packages/observable-hooks/__tests__/use-observable-state.spec.ts
index d5bf672f..c0516f98 100644
--- a/packages/observable-hooks/__tests__/use-observable-state.spec.ts
+++ b/packages/observable-hooks/__tests__/use-observable-state.spec.ts
@@ -1,6 +1,6 @@
 import { useObservableState, identity } from '../src'
 import { renderHook, act } from '@testing-library/react-hooks'
-import { of, Subject, throwError } from 'rxjs'
+import { BehaviorSubject, of, Subject, throwError } from 'rxjs'
 import { map, scan } from 'rxjs/operators'
 
 describe('useObservableState', () => {
@@ -51,6 +51,20 @@ describe('useObservableState', () => {
       expect(result.current[0]).toBe(1)
     })
 
+    it('should get the init state of BehaviorSubject without initialState', () => {
+      const value$ = new BehaviorSubject('22')
+      const { result } = renderHook(() => useObservableState(value$))
+      expect(result.current).toBe('22')
+    })
+
+    it('should ignore the manual initialState for BehaviorSubject', () => {
+      const value$ = new BehaviorSubject('22')
+      const { result } = renderHook(() =>
+        useObservableState(value$, 'initialState')
+      )
+      expect(result.current).toBe('22')
+    })
+
     it('should ignore the given init state when Observable also emits sync values', () => {
       const { result } = renderHook(() => useObservableState(() => of(1, 2), 3))
       expect(result.current[0]).toBe(2)
diff --git a/packages/observable-hooks/src/use-observable-state.ts b/packages/observable-hooks/src/use-observable-state.ts
index a8ebe151..f474bc87 100644
--- a/packages/observable-hooks/src/use-observable-state.ts
+++ b/packages/observable-hooks/src/use-observable-state.ts
@@ -41,22 +41,19 @@ import { useRefFn, getEmptySubject } from './helpers'
  *
  * @template TState Output state.
  *
- * @param input$ An Observable.
+ * @param input$ A BehaviorSubject.
  */
 export function useObservableState<TState>(
-  input$: Observable<TState>
-): TState | undefined
+  input$: BehaviorSubject<TState>
+): TState
 /**
  * @template TState Output state.
  *
- * @param input$ A BehaviorSubject.
- * @param initialState Optional initial state (defaults to the BehaviorSubject's value).
- * Can be the state value or a function that returns the state.
+ * @param input$ An Observable.
  */
 export function useObservableState<TState>(
-  input$: BehaviorSubject<TState>,
-  initialState?: TState | (() => TState)
-): TState
+  input$: Observable<TState>
+): TState | undefined
 /**
  * @template TState Output state.
  *
@@ -105,11 +102,7 @@ export function useObservableState<TState, TInput = TState>(
       ) => Observable<TState>),
   initialState?: TState | (() => TState)
 ): TState | undefined | [TState | undefined, (input: TInput) => void] {
-  const [state, setState] = useState<TState | undefined>(
-    state$OrInit instanceof BehaviorSubject 
-      ? state$OrInit.value 
-      : initialState
-  )
+  const [state, setState] = useState<TState | undefined>(initialState)
 
   let callback: undefined | ((input: TInput) => void)
   let state$: Observable<TState>