Replace class with a factory function

src/createStore.js

@@ -1,13 +1,63 @@
-import Store from './Store';
+import invariant from 'invariant';
+import isPlainObject from './utils/isPlainObject';
+
+// Don't ever try to handle these action types in your code. They are private.
+// For any unknown actions, you must return the current state.
+// If the current state is undefined, you must return the initial state.
+export const ActionTypes = {
+  INIT: '@@redux/INIT'
+};
 
 export default function createStore(reducer, initialState) {
-  const store = new Store(reducer, initialState);
+  invariant(
+    typeof reducer === 'function',
+    'Expected the reducer to be a function.'
+  );
+
+  let currentReducer = null;
+  let currentState = initialState;
+  let listeners = [];
+
+  function getState() {
+    return currentState;
+  }
+
+  function subscribe(listener) {
+    listeners.push(listener);
+
+    return function unsubscribe() {
+      const index = listeners.indexOf(listener);
+      listeners.splice(index, 1);
+    };
+  }
+
+  function dispatch(action) {
+    invariant(
+      isPlainObject(action),
+      'Actions must be plain objects. Use custom middleware for async actions.'
+    );
+
+    currentState = currentReducer(currentState, action);
+    listeners.forEach(listener => listener());
+    return action;
+  }
+
+  function getReducer() {
+    return currentReducer;
+  }
+
+  function replaceReducer(nextReducer) {
+    currentReducer = nextReducer;
+    dispatch({ type: ActionTypes.INIT });
+  }
+
+  replaceReducer(reducer);
 
   return {
-    dispatch: ::store.dispatch,
-    subscribe: ::store.subscribe,
-    getState: ::store.getState,
-    getReducer: ::store.getReducer,
-    replaceReducer: ::store.replaceReducer
+    dispatch,
+    subscribe,
+    getState,
+    getReducer,
+    replaceReducer
   };
 }

src/utils/combineReducers.js

@@ -1,7 +1,7 @@
 import mapValues from '../utils/mapValues';
 import pick from '../utils/pick';
 import invariant from 'invariant';
-import { ActionTypes } from '../Store';
+import { ActionTypes } from '../createStore';
 
 function getErrorMessage(key, action) {
   const actionType = action && action.type;

test/utils/combineReducers.spec.js

@@ -1,6 +1,6 @@
 import expect from 'expect';
 import { combineReducers } from '../../src';
-import { ActionTypes } from '../../src/Store';
+import { ActionTypes } from '../../src/createStore';
 
 describe('Utils', () => {
   describe('combineReducers', () => {