fix: improve TS types for createReducer, composeReducers and composeM…

…iddleware

src/composeMiddleware.d.ts

@@ -8,6 +8,116 @@ export function combineMiddlewareWithActionHandlers<
   ...middlewares: Middleware<DispatchExt, S, D>[]
 ): Middleware<DispatchExt, S, D>
 
+export default function composeMiddleware<
+  Ext1 = {},
+  S = any,
+  D extends Dispatch = Dispatch
+>(middleware1: Middleware<Ext1, S, D>): Middleware<Ext1, S, D>
+export default function composeMiddleware<
+  Ext1 = {},
+  Ext2 = {},
+  S = any,
+  D extends Dispatch = Dispatch
+>(
+  middleware1: Middleware<Ext1, S, D>,
+  middleware2: Middleware<Ext2, S, D>
+): Middleware<Ext1 & Ext2, S, D>
+export default function composeMiddleware<
+  Ext1 = {},
+  Ext2 = {},
+  Ext3 = {},
+  S = any,
+  D extends Dispatch = Dispatch
+>(
+  middleware1: Middleware<Ext1, S, D>,
+  middleware2: Middleware<Ext2, S, D>,
+  middleware3: Middleware<Ext3, S, D>
+): Middleware<Ext1 & Ext2 & Ext3, S, D>
+export default function composeMiddleware<
+  Ext1 = {},
+  Ext2 = {},
+  Ext3 = {},
+  Ext4 = {},
+  S = any,
+  D extends Dispatch = Dispatch
+>(
+  middleware1: Middleware<Ext1, S, D>,
+  middleware2: Middleware<Ext2, S, D>,
+  middleware3: Middleware<Ext3, S, D>,
+  middleware4: Middleware<Ext4, S, D>
+): Middleware<Ext1 & Ext2 & Ext3 & Ext4, S, D>
+export default function composeMiddleware<
+  Ext1 = {},
+  Ext2 = {},
+  Ext3 = {},
+  Ext4 = {},
+  Ext5 = {},
+  S = any,
+  D extends Dispatch = Dispatch
+>(
+  middleware1: Middleware<Ext1, S, D>,
+  middleware2: Middleware<Ext2, S, D>,
+  middleware3: Middleware<Ext3, S, D>,
+  middleware4: Middleware<Ext4, S, D>,
+  middleware5: Middleware<Ext5, S, D>
+): Middleware<Ext1 & Ext2 & Ext3 & Ext4 & Ext5, S, D>
+export default function composeMiddleware<
+  Ext1 = {},
+  Ext2 = {},
+  Ext3 = {},
+  Ext4 = {},
+  Ext5 = {},
+  Ext6 = {},
+  S = any,
+  D extends Dispatch = Dispatch
+>(
+  middleware1: Middleware<Ext1, S, D>,
+  middleware2: Middleware<Ext2, S, D>,
+  middleware3: Middleware<Ext3, S, D>,
+  middleware4: Middleware<Ext4, S, D>,
+  middleware5: Middleware<Ext5, S, D>,
+  middleware6: Middleware<Ext6, S, D>
+): Middleware<Ext1 & Ext2 & Ext3 & Ext4 & Ext5 & Ext6, S, D>
+export default function composeMiddleware<
+  Ext1 = {},
+  Ext2 = {},
+  Ext3 = {},
+  Ext4 = {},
+  Ext5 = {},
+  Ext6 = {},
+  Ext7 = {},
+  S = any,
+  D extends Dispatch = Dispatch
+>(
+  middleware1: Middleware<Ext1, S, D>,
+  middleware2: Middleware<Ext2, S, D>,
+  middleware3: Middleware<Ext3, S, D>,
+  middleware4: Middleware<Ext4, S, D>,
+  middleware5: Middleware<Ext5, S, D>,
+  middleware6: Middleware<Ext6, S, D>,
+  middleware7: Middleware<Ext7, S, D>
+): Middleware<Ext1 & Ext2 & Ext3 & Ext4 & Ext5 & Ext6 & Ext7, S, D>
+export default function composeMiddleware<
+  Ext1 = {},
+  Ext2 = {},
+  Ext3 = {},
+  Ext4 = {},
+  Ext5 = {},
+  Ext6 = {},
+  Ext7 = {},
+  Ext8 = {},
+  S = any,
+  D extends Dispatch = Dispatch
+>(
+  middleware1: Middleware<Ext1, S, D>,
+  middleware2: Middleware<Ext2, S, D>,
+  middleware3: Middleware<Ext3, S, D>,
+  middleware4: Middleware<Ext4, S, D>,
+  middleware5: Middleware<Ext5, S, D>,
+  middleware6: Middleware<Ext6, S, D>,
+  middleware7: Middleware<Ext7, S, D>,
+  middleware8: Middleware<Ext8, S, D>
+): Middleware<Ext1 & Ext2 & Ext3 & Ext4 & Ext5 & Ext6 & Ext7 & Ext8, S, D>
 export default function composeMiddleware<
   DispatchExt = {},
   S = any,

src/composeReducers.d.ts

@@ -1,11 +1,32 @@
 import { AnyAction, Reducer } from 'redux'
 
+type ReducerStateType<Reducer> = Reducer extends (
+  state: undefined | infer S0 extends {},
+  action: any
+) => infer S1
+  ? S0 | S1
+  : Reducer extends (state: infer S0 extends {}, action: any) => infer S1
+  ? S0 | S1
+  : never
+
+type ReducerActionType<Reducer> = Reducer extends (
+  state: any,
+  action: infer A extends AnyAction
+) => any
+  ? A
+  : never
+
 export function combineReducersWithActionHandlers<
-  S = any,
-  A extends AnyAction = AnyAction
->(...reducers: Reducer<S, A>[]): Reducer<S, A>
-
-export default function composeReducers<
-  S = any,
-  A extends AnyAction = AnyAction
->(...reducers: Reducer<S, A>[]): Reducer<S, A>[]
+  Reducers extends Reducer<any, any>[]
+>(...reducers: Reducers): composeReducers<Reducers>
+
+type composeReducers<Reducers extends Reducer<any, any>[]> = Reducer<
+  ReducerStateType<Reducers[number]>,
+  ReducerActionType<Reducers[number]>
+>
+
+declare function composeReducers<Reducers extends Reducer<any, any>[]>(
+  ...reducers: Reducers
+): composeReducers<Reducers>
+
+export default composeReducers

src/createReducer.d.ts

@@ -1,13 +1,44 @@
 import type { AnyAction, Reducer } from 'redux'
 
+type HandlersStateType<
+  Handlers extends Record<string, (state: any, action: any) => any>
+> = ReducerStateType<Handlers[keyof Handlers]>
+
+export type ReducerStateType<Reducer> = Reducer extends (
+  state: infer S0,
+  action: any
+) => infer S1
+  ? Exclude<S0, undefined> | S1
+  : never
+
+type HandlersActionType<
+  Handlers extends Record<string, (state: any, action: any) => any>
+> = ReducerActionType<Handlers[keyof Handlers]>
+
+export type ReducerActionType<Reducer> = Reducer extends (
+  state: any,
+  action: infer A extends AnyAction
+) => any
+  ? A
+  : never
+
+type AnyCoalesce<T, U> = 0 extends 1 & T ? U : T
+
+type ActionHandlers<S = any, A extends AnyAction = AnyAction> = {
+  [T in A['type']]?: (
+    state: S | undefined,
+    action: Extract<A, { type: T }>
+  ) => S
+}
+
+type InitializedActionHandlers<S = any, A extends AnyAction = AnyAction> = {
+  [T in A['type']]?: (state: S, action: Extract<A, { type: T }>) => S
+}
+
 export default function createReducer<S = any, A extends AnyAction = AnyAction>(
   initialState: S,
-  actionHandlers: Record<string, Reducer<S, A>>
+  actionHandlers: InitializedActionHandlers<S, A>
 ): Reducer<S, A>
 export default function createReducer<S = any, A extends AnyAction = AnyAction>(
-  actionHandlers: Record<string, Reducer<S, A>>
-): Reducer<S, A>
-export default function createReducer<S = any, A extends AnyAction = AnyAction>(
-  initialState: S,
-  actionHandlers: Record<string, Reducer<S, A>>
+  actionHandlers: ActionHandlers<S, A>
 ): Reducer<S, A>

test/typeTest.ts

@@ -0,0 +1,149 @@
+/* eslint-disable @typescript-eslint/no-unused-vars */
+import { Middleware, Reducer, applyMiddleware, createStore } from 'redux'
+import { composeMiddleware, composeReducers, createReducer } from '../src'
+
+export const LOGIN = 'login'
+export const LOGOUT = 'logout'
+
+export type LoginAction = {
+  type: typeof LOGIN
+  payload: {
+    password: string
+  }
+}
+export type LogoutAction = {
+  type: typeof LOGOUT
+  error?: true
+  payload?: {
+    error?: string
+  }
+}
+
+export type AuthAction = LoginAction | LogoutAction
+
+export type Auth = {
+  error: string | undefined
+}
+
+export const reducer1: Reducer<Auth, AuthAction> = createReducer<
+  Auth,
+  AuthAction
+>(
+  { error: undefined },
+  {
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    [LOGIN]: (state, action) => ({
+      error: undefined,
+    }),
+    [LOGOUT]: (state, { payload }) => ({
+      error: payload?.error,
+    }),
+  }
+)
+
+export const reducer2: Reducer<Auth, AuthAction> = createReducer<
+  Auth,
+  AuthAction
+>({
+  // eslint-disable-next-line @typescript-eslint/no-unused-vars
+  [LOGIN]: (state, action) => ({
+    error: undefined,
+  }),
+  [LOGOUT]: (state, { payload }) => ({
+    error: payload?.error,
+  }),
+})
+
+export const reducer3: Reducer<Auth, AuthAction> = createReducer<
+  Auth,
+  AuthAction
+>(
+  { error: undefined },
+  {
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    [LOGIN]: (state: Auth, action: LoginAction) => ({
+      error: undefined,
+    }),
+    [LOGOUT]: (state: Auth, { payload }: LogoutAction) => ({
+      error: payload?.error,
+    }),
+  }
+)
+
+export const reducer4: Reducer<Auth, AuthAction> = createReducer<
+  Auth,
+  AuthAction
+>({
+  // eslint-disable-next-line @typescript-eslint/no-unused-vars
+  [LOGIN]: (state: Auth | undefined, action: LoginAction) => ({
+    error: undefined,
+  }),
+  [LOGOUT]: (state: Auth | undefined, { payload }: LogoutAction) => ({
+    error: payload?.error,
+  }),
+})
+
+export const reducer5 = composeReducers(
+  createReducer<Auth, LoginAction>({
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    [LOGIN]: (state: Auth | undefined, action: LoginAction) => ({
+      error: undefined,
+    }),
+  }),
+  createReducer<Auth, LogoutAction>({
+    [LOGOUT]: (state: Auth | undefined, { payload }: LogoutAction) => ({
+      error: payload?.error,
+    }),
+  })
+)
+
+export const reducer6: Reducer<Auth, AuthAction> = composeReducers(
+  createReducer<Auth, LoginAction>({
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    [LOGIN]: (state: Auth | undefined, action: LoginAction) => ({
+      error: undefined,
+    }),
+  }),
+  createReducer<Auth, LogoutAction>({
+    [LOGOUT]: (state: Auth | undefined, { payload }: LogoutAction) => ({
+      error: payload?.error,
+    }),
+  })
+)
+
+type AsyncAction<V> = {
+  type: 'async'
+  perform: () => Promise<V>
+}
+
+const asyncActionMiddleware: Middleware<
+  {
+    <V>(action: AsyncAction<V>): Promise<V>
+  },
+  Auth
+> = (store) => (next) => (action) => null as any
+
+type FooAction = {
+  type: 'foo'
+}
+
+const fooActionMiddleware: Middleware<
+  {
+    (action: FooAction): 'foo'
+  },
+  Auth
+> = (store) => (next) => (action) => null as any
+
+const store = applyMiddleware(
+  composeMiddleware(asyncActionMiddleware, fooActionMiddleware)
+)(createStore)(reducer1)
+
+const value1: 'foo' = store.dispatch({ type: 'foo' })
+const value2: Promise<number> = store.dispatch({
+  type: 'async',
+  perform: async () => 3,
+})
+const value3: LoginAction = store.dispatch({
+  type: 'login',
+  payload: { password: 'foo' },
+})

tsconfig.json

@@ -1,6 +1,6 @@
 {
   "extends": "./node_modules/@jcoreio/toolchain-typescript/tsconfig.json",
-  "include": ["./src"],
+  "include": ["./src", "./test"],
   "exclude": ["node_modules"],
   "compilerOptions": {
     "skipLibCheck": false