main.js

// Modules to control application life and create native browser window
const {app, BrowserWindow} = require('electron')

// Keep a global reference of the window object, if you don't, the window will be closed automatically when the JavaScript object is garbage collected.
let mainWindow

function createWindow () {
  // Create the browser window
  mainWindow = new BrowserWindow()

  // and load the index.html of the app.
  mainWindow.loadFile('index.html')

  // Make fullscreen
  // Source: https://discuss.atom.io/t/how-to-open-the-window-in-fullscreen-mode-when-the-app-starts/17083/2
  mainWindow.maximize()

  // Open the DevTools.
  //mainWindow.webContents.openDevTools()

  // Emitted when the window is closed.
  mainWindow.on('closed', function () {
    // Dereference the window object, usually you would store windows in an array if your app supports multi windows, this is the time when you should delete the corresponding element.
    mainWindow = null
  })
}

// This method will be called when Electron has finished initialization and is ready to create browser windows. Some APIs can only be used after this event occurs.
app.on('ready', createWindow)

// Quit when all windows are closed.
app.on('window-all-closed', function () {
  // On OS X it is common for applications and their menu bar to stay active until the user quits explicitly with Cmd + Q
  if (process.platform !== 'darwin') {
    app.quit()
  }
})

app.on('activate', function () {
  // On OS X it's common to re-create a window in the app when the dock icon is clicked and there are no other windows open.
  if (mainWindow === null) {
    createWindow()
  }
})