Fixed combineReducers changeDetection logic(reduxjs#3488)

anubhavgupta · Jul 31, 2019 · 001a197 · 001a197
1 parent 59cc278
commit 001a197
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diff --git a/src/combineReducers.js b/src/combineReducers.js
@@ -173,6 +173,8 @@ export default function combineReducers(reducers) {
       nextState[key] = nextStateForKey
       hasChanged = hasChanged || nextStateForKey !== previousStateForKey
     }
+    hasChanged =
+      hasChanged || finalReducerKeys.length !== Object.keys(state).length
     return hasChanged ? nextState : state
   }
 }
diff --git a/test/combineReducers.spec.js b/test/combineReducers.spec.js
@@ -281,5 +281,56 @@ describe('Utils', () => {
       spy.mockClear()
       console.error = preSpy
     })
+
+    describe('With Replace Reducers', function() {
+      const foo = (state = {}) => state
+      const bar = (state = {}) => state
+      const ACTION = { type: 'ACTION' }
+
+      it('should return an updated state when additional reducers are passed to combineReducers', function() {
+        const originalCompositeReducer = combineReducers({ foo })
+        const store = createStore(originalCompositeReducer)
+        store.dispatch(ACTION)
+        const initialState = store.getState()
+        store.replaceReducer(combineReducers({ foo, bar }))
+        store.dispatch(ACTION)
+        const nextState = store.getState()
+        expect(nextState).not.toBe(initialState)
+      })
+
+      it('should return an updated state when reducers passed to combineReducers are changed', function() {
+        const baz = (state = {}) => state
+
+        const originalCompositeReducer = combineReducers({ foo, bar })
+        const store = createStore(originalCompositeReducer)
+        store.dispatch(ACTION)
+        const initialState = store.getState()
+        store.replaceReducer(combineReducers({ baz, bar }))
+        store.dispatch(ACTION)
+        const nextState = store.getState()
+        expect(nextState).not.toBe(initialState)
+      })
+
+      it('should return the same state when reducers passed to combineReducers not changed', function() {
+        const originalCompositeReducer = combineReducers({ foo, bar })
+        const store = createStore(originalCompositeReducer)
+        store.dispatch(ACTION)
+        const initialState = store.getState()
+        store.replaceReducer(combineReducers({ foo, bar }))
+        store.dispatch(ACTION)
+        const nextState = store.getState()
+        expect(nextState).toBe(initialState)
+      })
+
+      it('should return an updated state when one of more reducers passed to the combineReducers are removed', function() {
+        const originalCompositeReducer = combineReducers({ foo, bar })
+        const store = createStore(originalCompositeReducer)
+        store.dispatch(ACTION)
+        const initialState = store.getState()
+        store.replaceReducer(combineReducers({ bar }))
+        const nextState = store.getState()
+        expect(nextState).not.toBe(initialState)
+      })
+    })
   })
 })