electron/docs/fiddles/native-ui/dialogs/open-file-or-directory/main.js

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

// 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({
    width: 800,
    height: 600,
    webPreferences: {
      contextIsolation: false,
      nodeIntegration: true
    }
  })

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

  // 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
  })

  // Open external links in the default browser
  mainWindow.webContents.on('will-navigate', (event, url) => {
    event.preventDefault()
    shell.openExternal(url)
  })
}

// 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(createWindow)

// Quit when all windows are closed.
app.on('window-all-closed', function () {
  // On macOS 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 macOS it is 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()
  }
})

ipcMain.on('open-file-dialog', event => {
  dialog.showOpenDialog(
    {
      properties: ['openFile', 'openDirectory']
    },
    files => {
      if (files) {
        event.sender.send('selected-directory', files)
      }
    }
  )
})

// 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.