Add support for merging intitial state into rehydrated state

package.json

@@ -28,6 +28,9 @@
   "peerDependencies": {
     "@ngrx/store": "^4.0.0 || ^5.0.0"
   },
+  "dependencies": {
+    "deepmerge": "^2.1.0"
+  },
   "devDependencies": {
     "@angular/core": "^2.4.7",
     "@ngrx/core": "^1.2.0",

spec/index_spec.ts

@@ -1,6 +1,6 @@
 declare var beforeEachProviders, it, describe, expect, inject;
 require('es6-shim');
-import { syncStateUpdate, rehydrateApplicationState, dateReviver } from '../src/index';
+import { syncStateUpdate, rehydrateApplicationState, dateReviver, mergeInitialState } from '../src/index';
 import *  as CryptoJS from 'crypto-js';
 
 // Very simple classes to test serialization options.  They cover string, number, date, and nested classes
@@ -374,4 +374,34 @@ describe('ngrxLocalStorage', () => {
         expect(t1 instanceof TypeA).toBeTruthy();
         expect(finalState.simple instanceof TypeA).toBeFalsy();
     });
+
+    it('mergeInitialState', () => {
+        // test that nested object are merged, not overwritten
+        let s = new MockStorage();
+        let skr = mockStorageKeySerializer;
+        let initialState = { state: { stored: false, not_stored: false }};
+        let keys = [{ state: ['stored']}];
+        let mock_action = { type: '@ngrx/store/init' };
+
+        // write the initial state,
+        // key "not_stored" will not be included in hydrated state
+        syncStateUpdate(initialState, keys, s, skr, false);
+        let rehydratedState: any = rehydrateApplicationState(keys, s, skr, true);
+        expect(rehydratedState.state.stored).toEqual(false);
+        expect(rehydratedState.state.not_stored).not.toBeDefined();
+
+        // update this state,
+        // "not_stored" still not present
+        let newState = { state: { ...initialState.state, stored: true, not_stored: true } };
+        syncStateUpdate(newState, keys, s, skr, false);
+
+        let newRehydratedState: any = rehydrateApplicationState(keys, s, skr, true);
+        expect(newRehydratedState.state.stored).toEqual(true);
+        expect(newRehydratedState.state.not_stored).not.toBeDefined();
+
+        // merge state with initialstate. now "not_stored" is included with default value
+        let mergedState = mergeInitialState({}, initialState, newRehydratedState, mock_action);
+        expect(mergedState.state.stored).toEqual(true);
+        expect(mergedState.state.not_stored).toEqual(false);
+    });
 });

src/index.ts

@@ -1,3 +1,5 @@
+import * as merge from 'deepmerge';
+
 const INIT_ACTION = '@ngrx/store/init';
 const UPDATE_ACTION = '@ngrx/store/update-reducers';
 const detectDate = /(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2}):(\d{2})/;
@@ -228,12 +230,8 @@ export const localStorageSync = (config: LocalStorageConfig) => (
          Handle case where state is rehydrated AND initial state is supplied.
          Any additional state supplied will override rehydrated state for the given key.
          */
-    if (
-      (action.type === INIT_ACTION || action.type === UPDATE_ACTION) &&
-      rehydratedState
-    ) {
-      state = Object.assign({}, state, rehydratedState);
-    }
+    state = mergeInitialState(state, config.initialState, rehydratedState, action);
+
     const nextState = reducer(state, action);
     syncStateUpdate(
       nextState,
@@ -246,6 +244,16 @@ export const localStorageSync = (config: LocalStorageConfig) => (
   };
 };
 
+export const mergeInitialState = (state, initialState, rehydratedState, action) => {
+  if (
+    (action.type === INIT_ACTION || action.type === UPDATE_ACTION) &&
+    rehydratedState
+  ) {
+    return merge.all([state, initialState || {}, rehydratedState]);
+  }
+  return state;
+}
+
 /*
     @deprecated: Use localStorageSync(LocalStorageConfig)
 
@@ -272,6 +280,7 @@ export interface LocalStorageConfig {
   keys: any[];
   rehydrate?: boolean;
   storage?: Storage;
+  initialState?: any;
   removeOnUndefined?: boolean;
   restoreDates?: boolean;
   storageKeySerializer?: (key: string) => string;