second commit :S

src/Reducers/index.js

@@ -4,10 +4,11 @@ import { combineReducers } from 'redux';
 import {
   UPDATE_TEXT,
   TOGGLE_EDITORS,
+  TOGGLE_HISTORY_SIDEBAR,
   ActiveEditors,
 } from '../Actions';
 
-function activeEditors(state = [ActiveEditors.MARKDOWN, ActiveEditors.TEXT], action) {
+const activeEditors = (state = [ActiveEditors.MARKDOWN, ActiveEditors.TEXT], action) => {
   switch (action.type) {
     case TOGGLE_EDITORS: {
       const newState = _.xor(state, [action.toggledEditor]);
@@ -22,7 +23,20 @@ function activeEditors(state = [ActiveEditors.MARKDOWN, ActiveEditors.TEXT], act
   }
 }
 
-function text(state = '', action) {
+const historySidebar = (state = { visible: false }, action) => {
+  switch (action.type) {
+    case TOGGLE_HISTORY_SIDEBAR: {
+      return {
+        ...state,
+        visible: !state.visible,
+      };
+    }
+    default:
+      return state;
+  }
+}
+
+const text = (state = '', action) => {
   switch (action.type) {
     case UPDATE_TEXT:
       return action.text;
@@ -31,9 +45,8 @@ function text(state = '', action) {
   }
 }
 
-const application = combineReducers({
+export default combineReducers({
   activeEditors,
+  historySidebar,
   text,
 });
-
-export default application;