fix(Store): only default to initialValue when store value is undefined (#886)

Author: jbedard

modules/store/spec/store.spec.ts

@@ -68,6 +68,76 @@ describe('ngRx Store', () => {
         complete: done,
       });
     });
+
+    function testInitialState(feature?: string) {
+      store = TestBed.get(Store);
+      dispatcher = TestBed.get(ActionsSubject);
+
+      const actionSequence = '--a--b--c--d--e--f--g';
+      const stateSequence = 'i-w-----x-----y--z---';
+      const actionValues = {
+        a: { type: INCREMENT },
+        b: { type: 'OTHER' },
+        c: { type: RESET },
+        d: { type: 'OTHER' }, //reproduces https://github.com/ngrx/platform/issues/880 because state is falsey
+        e: { type: INCREMENT },
+        f: { type: INCREMENT },
+        g: { type: 'OTHER' },
+      };
+      const counterSteps = hot(actionSequence, actionValues);
+      counterSteps.subscribe(action => store.dispatch(action));
+
+      const counterStateWithString = feature
+        ? (store as any).select(feature, 'counter1')
+        : store.select('counter1');
+
+      const counter1Values = { i: 1, w: 2, x: 0, y: 1, z: 2 };
+
+      expect(counterStateWithString).toBeObservable(
+        hot(stateSequence, counter1Values)
+      );
+    }
+
+    it('should reset to initial state when undefined (root ActionReducerMap)', () => {
+      TestBed.configureTestingModule({
+        imports: [
+          StoreModule.forRoot(
+            { counter1: counterReducer },
+            { initialState: { counter1: 1 } }
+          ),
+        ],
+      });
+
+      testInitialState();
+    });
+
+    it('should reset to initial state when undefined (feature ActionReducer)', () => {
+      TestBed.configureTestingModule({
+        imports: [
+          StoreModule.forRoot({}),
+          StoreModule.forFeature('counter1', counterReducer, {
+            initialState: 1,
+          }),
+        ],
+      });
+
+      testInitialState();
+    });
+
+    it('should reset to initial state when undefined (feature ActionReducerMap)', () => {
+      TestBed.configureTestingModule({
+        imports: [
+          StoreModule.forRoot({}),
+          StoreModule.forFeature(
+            'feature1',
+            { counter1: counterReducer },
+            { initialState: { counter1: 1 } }
+          ),
+        ],
+      });
+
+      testInitialState('feature1');
+    });
   });
 
   describe('basic store actions', () => {

modules/store/src/reducer_manager.ts

@@ -43,7 +43,7 @@ export class ReducerManager extends BehaviorSubject<ActionReducer<any, any>>
       typeof reducers === 'function'
         ? (state: any, action: any) =>
             createFeatureReducer(reducers, metaReducers)(
-              state || initialState,
+              state === undefined ? initialState : state,
               action
             )
         : createReducerFactory(reducerFactory, metaReducers)(

modules/store/src/utils.ts

@@ -27,7 +27,7 @@ export function combineReducers(
   const finalReducerKeys = Object.keys(finalReducers);
 
   return function combination(state, action) {
-    state = state || initialState;
+    state = state === undefined ? initialState : state;
     let hasChanged = false;
     const nextState: any = {};
     for (let i = 0; i < finalReducerKeys.length; i++) {