main.js

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

function createWindow (railsApp) {
  // Create the browser window.
  const mainWindow = new BrowserWindow({
    width: 800,
    height: 600,
    webPreferences: {
      preload: path.join(__dirname, 'preload.js')
    }
  })

  // and load the index.html of the app.
  mainWindow.loadURL('http://localhost:3000')

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

   // Emitted when the window is closed.
   mainWindow.on('closed', function() {
    railsApp.kill('SIGINT')
  })
}

// 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.whenReady().then(() => {
  const railsApp = require('child_process').spawn('rails', ['s'])

  console.log("starting rails server... waiting 5 seconds")

  async function start() {
    const res = await fetch('http://localhost:3000')
    console.log('rails server started')
    createWindow(railsApp)
    app.on('activate', function () {
      // On macOS 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 (BrowserWindow.getAllWindows().length === 0) createWindow(railsApp)
    })
  }

  setTimeout(() => start(), 5000)
})

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

// In this file you can include the rest of your app's specific main process
// code. You can also put them in separate files and require them here.