main.js

const electron = require('electron')

const app = electron.app

const BrowserWindow = electron.BrowserWindow

if (process.env.NODE_ENV === 'development') {
  require('electron-reload')(__dirname, {
    electron: require(`${__dirname}/node_modules/electron`)
  })
}

let mainWindow

function createWindow () {
  // Create the browser window.
  mainWindow = new BrowserWindow({width: 800, height: 600, icon: './cpu.png'})

  // and load the index.html of the app.
  if (process.env.NODE_ENV === 'development') {
    mainWindow.loadURL(`http://localhost:3000`)
  } else {
    mainWindow.loadURL(`file://${__dirname}/index.html`)
  }

  // Open the DevTools.
  if (process.env.NODE_ENV === 'development') {
    mainWindow.webContents.openDevTools()
  }

  // Emitted when the window is closed.
  mainWindow.on('closed', function () {
    mainWindow = null
  })
}

// This method will be called when Electron has finished
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
  if (process.platform !== 'darwin') {
    app.quit()
  }
})

app.on('activate', function () {
  if (mainWindow === null) {
    createWindow()
  }
})