Relaunch the app when the icon is clicked on Mac

On macOS, if an app is not fully closed, it is expected to open again
when the icon is clicked.

main.js

@@ -15,17 +15,40 @@ initGlobalLogger()
 
 let mainWindow = null
 
-app.on('ready', () => {
+function createWindow () {
   mainWindow = new BrowserWindow({
-      width: 1000,
-      height: 700,
-      minWidth: 1000,
-      minHeight: 700,
-      titleBarStyle: 'hidden'
+    width: 1000,
+    height: 700,
+    minWidth: 1000,
+    minHeight: 700,
+    titleBarStyle: 'hidden'
   })
   mainWindow.loadURL(`file://${__dirname}/index.html`)
+  setUpApplicationMenu()
   // mainWindow.webContents.openDevTools()
+}
+
+app.on('ready', createWindow)
+
+app.on('window-all-closed', function() {
+  logger.info('The app window is closed')
+  if (process.platform !== 'darwin') app.quit()
+  mainWindow = null
+})
 
+app.on('before-quit', function() {
+
+})
+
+app.on('activate', () => {
+  // On macOS, if an app is not fully closed, it is expected to open again
+  // when the icon is clicked.
+  if (process.platform === 'darwin' && mainWindow === null) {
+    createWindow()
+  }
+})
+
+function setUpApplicationMenu () {
   // Create the Application's main menu
   let template = [{
     label: "Application",
@@ -46,24 +69,7 @@ app.on('ready', () => {
     ]}
   ]
   Menu.setApplicationMenu(Menu.buildFromTemplate(template))
-})
-
-app.on('window-all-closed', function() {
-  logger.info('The app window is closed')
-  // mainWindow.webContents.session.clearStorageData([
-  //     'appcache',
-  //     'cookies',
-  //     'indexdb',
-  //     'shadercache',
-  //     'websql',
-  //     'serviceworkers',
-  //   ], () => {})
-  if (process.platform !== 'darwin') app.quit()
-})
-
-app.on('before-quit', function() {
-
-})
+}
 
 function initGlobalLogger () {
   logger.level = 'debug'