electron/docs/fiddles/system/clipboard/copy/main.js

const { app, BrowserWindow, ipcMain, clipboard } = require('electron')
const path = require('path')

let mainWindow = null

function createWindow () {
  const windowOptions = {
    width: 600,
    height: 400,
    title: 'Clipboard copy',
    webPreferences: {
      preload: path.join(__dirname, 'preload.js')
    }
  }

  mainWindow = new BrowserWindow(windowOptions)
  mainWindow.loadFile('index.html')

  mainWindow.on('closed', () => {
    mainWindow = null
  })
}

ipcMain.handle('clipboard:writeText', (event, text) => {
  clipboard.writeText(text)
})

app.whenReady().then(() => {
  createWindow()
  
  app.on('activate', function () {
    if (BrowserWindow.getAllWindows().length === 0) createWindow()
  })
})

app.on('window-all-closed', function () {
  if (process.platform !== 'darwin') app.quit()
})