Implement combinedReducers from scratch

src/combinedReducers.js

@@ -0,0 +1,15 @@
+export const combineReducers = reducers => {
+    // Reduce all keys for reducers from 'todos' and 'visibilityFilter'
+    return (state = {}, action) => {
+        return Object.keys(reducers).reduce( 
+            (nextState, key) => {
+                nextState[key] = reducers[key](
+                    state[key],
+                    action
+                );
+                return nextState;
+            },
+            {} // iniital empty object
+        );
+    };
+};

src/index.js

@@ -1,6 +1,6 @@
 import React from 'react';
-import { combineReducers } from 'redux';
-import {createStore} from './createStore';
+import { combineReducers } from './combinedReducers';
+import {  createStore   } from './createStore';
 import ReactDOM from 'react-dom';
 import './index.css';