convert combineReducers test

index.d.ts

@@ -326,7 +326,9 @@ export interface Store<S = any, A extends Action = AnyAction> {
    *
    * @param nextReducer The reducer for the store to use instead.
    */
-  replaceReducer(nextReducer: Reducer<S, A>): void
+  replaceReducer<NewState = S, NewActions extends A = A>(
+    nextReducer: Reducer<NewState, NewActions>
+  ): Store<NewState, NewActions>
 
   /**
    * Interoperability point for observable/reactive libraries.
@@ -667,3 +669,9 @@ export function compose<R>(
 ): (...args: any[]) => R
 
 export function compose<R>(...funcs: Function[]): (...args: any[]) => R
+
+export const __DO_NOT_USE__ActionTypes: {
+  INIT: string
+  REPLACE: string
+  PROBE_UNKNOWN_ACTION: () => string
+}

src/createStore.js

@@ -238,6 +238,7 @@ export default function createStore(reducer, preloadedState, enhancer) {
     // will receive the previous state. This effectively populates
     // the new state tree with any relevant data from the old one.
     dispatch({ type: ActionTypes.REPLACE })
+    return store
   }
 
   /**
@@ -284,11 +285,12 @@ export default function createStore(reducer, preloadedState, enhancer) {
   // the initial state tree.
   dispatch({ type: ActionTypes.INIT })
 
-  return {
+  const store = {
     dispatch,
     subscribe,
     getState,
     replaceReducer,
     [$$observable]: observable
   }
+  return store
 }

test/combineReducers.spec.js → test/combineReducers.spec.ts

@@ -2,34 +2,40 @@
 import {
   createStore,
   combineReducers,
-  __DO_NOT_USE__ActionTypes as ActionTypes
-} from '../'
+  Reducer,
+  AnyAction,
+  __DO_NOT_USE__ActionTypes as ActionTypes,
+  CombinedState
+} from '..'
 
 describe('Utils', () => {
   describe('combineReducers', () => {
     it('returns a composite reducer that maps the state keys to given reducers', () => {
       const reducer = combineReducers({
-        counter: (state = 0, action) =>
+        counter: (state: number = 0, action) =>
           action.type === 'increment' ? state + 1 : state,
-        stack: (state = [], action) =>
+        stack: (state: any[] = [], action) =>
           action.type === 'push' ? [...state, action.value] : state
       })
 
-      const s1 = reducer({}, { type: 'increment' })
+      const s1 = reducer(undefined, { type: 'increment' })
       expect(s1).toEqual({ counter: 1, stack: [] })
       const s2 = reducer(s1, { type: 'push', value: 'a' })
       expect(s2).toEqual({ counter: 1, stack: ['a'] })
     })
 
     it('ignores all props which are not a function', () => {
+      // we double-cast because these conditions can only happen in a javascript setting
       const reducer = combineReducers({
-        fake: true,
-        broken: 'string',
-        another: { nested: 'object' },
+        fake: (true as unknown) as Reducer,
+        broken: ('string' as unknown) as Reducer,
+        another: ({ nested: 'object' } as unknown) as Reducer,
         stack: (state = []) => state
       })
 
-      expect(Object.keys(reducer({}, { type: 'push' }))).toEqual(['stack'])
+      expect(Object.keys(reducer(undefined, { type: 'push' }))).toEqual([
+        'stack'
+      ])
     })
 
     it('warns if a reducer prop is undefined', () => {
@@ -55,7 +61,7 @@ describe('Utils', () => {
 
     it('throws an error if a reducer returns undefined handling an action', () => {
       const reducer = combineReducers({
-        counter(state = 0, action) {
+        counter(state: number = 0, action) {
           switch (action && action.type) {
             case 'increment':
               return state + 1
@@ -77,12 +83,14 @@ describe('Utils', () => {
       expect(() => reducer({ counter: 0 }, null)).toThrow(
         /"counter".*an action/
       )
-      expect(() => reducer({ counter: 0 }, {})).toThrow(/"counter".*an action/)
+      expect(() =>
+        reducer({ counter: 0 }, ({} as unknown) as AnyAction)
+      ).toThrow(/"counter".*an action/)
     })
 
     it('throws an error on first call if a reducer returns undefined initializing', () => {
       const reducer = combineReducers({
-        counter(state, action) {
+        counter(state: number, action) {
           switch (action.type) {
             case 'increment':
               return state + 1
@@ -93,7 +101,9 @@ describe('Utils', () => {
           }
         }
       })
-      expect(() => reducer({})).toThrow(/"counter".*initialization/)
+      expect(() => reducer(undefined, { type: '' })).toThrow(
+        /"counter".*initialization/
+      )
     })
 
     it('catches error thrown in reducer when initializing and re-throw', () => {
@@ -102,14 +112,16 @@ describe('Utils', () => {
           throw new Error('Error thrown in reducer')
         }
       })
-      expect(() => reducer({})).toThrow(/Error thrown in reducer/)
+      expect(() =>
+        reducer(undefined, (undefined as unknown) as AnyAction)
+      ).toThrow(/Error thrown in reducer/)
     })
 
     it('allows a symbol to be used as an action type', () => {
       const increment = Symbol('INCREMENT')
 
       const reducer = combineReducers({
-        counter(state = 0, action) {
+        counter(state: number = 0, action) {
           switch (action.type) {
             case increment:
               return state + 1
@@ -135,7 +147,7 @@ describe('Utils', () => {
         }
       })
 
-      const initialState = reducer(undefined, '@@INIT')
+      const initialState = reducer(undefined, { type: '@@INIT' })
       expect(reducer(initialState, { type: 'FOO' })).toBe(initialState)
     })
 
@@ -144,7 +156,7 @@ describe('Utils', () => {
         child1(state = {}) {
           return state
         },
-        child2(state = { count: 0 }, action) {
+        child2(state: { count: number } = { count: 0 }, action) {
           switch (action.type) {
             case 'increment':
               return { count: state.count + 1 }
@@ -157,15 +169,15 @@ describe('Utils', () => {
         }
       })
 
-      const initialState = reducer(undefined, '@@INIT')
+      const initialState = reducer(undefined, { type: '@@INIT' })
       expect(reducer(initialState, { type: 'increment' })).not.toBe(
         initialState
       )
     })
 
     it('throws an error on first call if a reducer attempts to handle a private action', () => {
       const reducer = combineReducers({
-        counter(state, action) {
+        counter(state: number, action) {
           switch (action.type) {
             case 'increment':
               return state + 1
@@ -179,7 +191,9 @@ describe('Utils', () => {
           }
         }
       })
-      expect(() => reducer()).toThrow(/"counter".*private/)
+      expect(() =>
+        reducer(undefined, (undefined as unknown) as AnyAction)
+      ).toThrow(/"counter".*private/)
     })
 
     it('warns if no reducers are passed to combineReducers', () => {
@@ -188,7 +202,7 @@ describe('Utils', () => {
       console.error = spy
 
       const reducer = combineReducers({})
-      reducer({})
+      reducer(undefined, { type: '' })
       expect(spy.mock.calls[0][0]).toMatch(
         /Store does not have a valid reducer/
       )
@@ -200,9 +214,17 @@ describe('Utils', () => {
     it('warns if input state does not match reducer shape', () => {
       const preSpy = console.error
       const spy = jest.fn()
+      const nullAction = (undefined as unknown) as AnyAction
       console.error = spy
 
-      const reducer = combineReducers({
+      interface ShapeState {
+        foo: { bar: number }
+        baz: { qux: number }
+      }
+
+      type ShapeMismatchState = CombinedState<ShapeState>
+
+      const reducer = combineReducers<ShapeState>({
         foo(state = { bar: 1 }) {
           return state
         },
@@ -211,44 +233,51 @@ describe('Utils', () => {
         }
       })
 
-      reducer()
+      reducer(undefined, nullAction)
       expect(spy.mock.calls.length).toBe(0)
 
-      reducer({ foo: { bar: 2 } })
+      reducer(({ foo: { bar: 2 } } as unknown) as ShapeState, nullAction)
       expect(spy.mock.calls.length).toBe(0)
 
-      reducer({
-        foo: { bar: 2 },
-        baz: { qux: 4 }
-      })
+      reducer(
+        {
+          foo: { bar: 2 },
+          baz: { qux: 4 }
+        },
+        nullAction
+      )
       expect(spy.mock.calls.length).toBe(0)
 
-      createStore(reducer, { bar: 2 })
+      createStore(reducer, ({ bar: 2 } as unknown) as ShapeState)
       expect(spy.mock.calls[0][0]).toMatch(
         /Unexpected key "bar".*createStore.*instead: "foo", "baz"/
       )
 
-      createStore(reducer, { bar: 2, qux: 4, thud: 5 })
+      createStore(reducer, ({
+        bar: 2,
+        qux: 4,
+        thud: 5
+      } as unknown) as ShapeState)
       expect(spy.mock.calls[1][0]).toMatch(
         /Unexpected keys "qux", "thud".*createStore.*instead: "foo", "baz"/
       )
 
-      createStore(reducer, 1)
+      createStore(reducer, (1 as unknown) as ShapeState)
       expect(spy.mock.calls[2][0]).toMatch(
         /createStore has unexpected type of "Number".*keys: "foo", "baz"/
       )
 
-      reducer({ corge: 2 })
+      reducer(({ corge: 2 } as unknown) as ShapeState, nullAction)
       expect(spy.mock.calls[3][0]).toMatch(
         /Unexpected key "corge".*reducer.*instead: "foo", "baz"/
       )
 
-      reducer({ fred: 2, grault: 4 })
+      reducer(({ fred: 2, grault: 4 } as unknown) as ShapeState, nullAction)
       expect(spy.mock.calls[4][0]).toMatch(
         /Unexpected keys "fred", "grault".*reducer.*instead: "foo", "baz"/
       )
 
-      reducer(1)
+      reducer((1 as unknown) as ShapeState, nullAction)
       expect(spy.mock.calls[5][0]).toMatch(
         /reducer has unexpected type of "Number".*keys: "foo", "baz"/
       )
@@ -261,25 +290,32 @@ describe('Utils', () => {
       const preSpy = console.error
       const spy = jest.fn()
       console.error = spy
+      const nullAction = { type: '' }
 
       const foo = (state = { foo: 1 }) => state
       const bar = (state = { bar: 2 }) => state
 
       expect(spy.mock.calls.length).toBe(0)
 
+      interface WarnState {
+        foo: { foo: number }
+        bar: { bar: number }
+      }
+
       const reducer = combineReducers({ foo, bar })
-      const state = { foo: 1, bar: 2, qux: 3 }
+      const state = ({ foo: 1, bar: 2, qux: 3 } as unknown) as WarnState
+      const bazState = ({ ...state, baz: 5 } as unknown) as WarnState
 
-      reducer(state, {})
-      reducer(state, {})
-      reducer(state, {})
-      reducer(state, {})
+      reducer(state, nullAction)
+      reducer(state, nullAction)
+      reducer(state, nullAction)
+      reducer(state, nullAction)
       expect(spy.mock.calls.length).toBe(1)
 
-      reducer({ ...state, baz: 5 }, {})
-      reducer({ ...state, baz: 5 }, {})
-      reducer({ ...state, baz: 5 }, {})
-      reducer({ ...state, baz: 5 }, {})
+      reducer(bazState, nullAction)
+      reducer({ ...bazState }, nullAction)
+      reducer({ ...bazState }, nullAction)
+      reducer({ ...bazState }, nullAction)
       expect(spy.mock.calls.length).toBe(2)
 
       spy.mockClear()