old_contents: 
  import path from 'path';
  import {app, ipcMain, BrowserWindow} from 'electron';
  import connect from 'electron-connect';
  
  // constant variable ==========================================================
  const IS_DEVELOPMENT = __MODE__ === 'development';
  const INDEX_HTML_PATH = IS_DEVELOPMENT ? './app/client/index.html' : './client/index.html';
  const MAIN_WINDOW_PARAMETER = {
      width: 1200,
      height: 800,
      frame: false,
      webPreferences: {
          nodeIntegration: true
      }
  };
  
  // variables ==================================================================
  let mainWindow;    // main window
  let connectClient; // connector from electron-connect for client
  
  // app events =================================================================
  let isLockable = app.requestSingleInstanceLock();
  if(isLockable !== true){app.quit();}
  
  app.on('second-instance', () => {
      if(mainWindow != null){
          if(mainWindow.isMinimized() === true){
              mainWindow.restore();
          }
          mainWindow.focus();
      }
  });
  
  app.on('ready', () => {
      createMainWindow();
  });
  
  app.on('window-all-closed', () => {
      mainWindow = null;
      app.quit();
  });
  
  // function ===================================================================
  function createMainWindow(){
      // create new browser window
      mainWindow = new BrowserWindow(MAIN_WINDOW_PARAMETER);
      mainWindow.loadFile(INDEX_HTML_PATH);
  
      mainWindow.on('closed', () => {
          mainWindow = null;
          if(IS_DEVELOPMENT === true){
              connectClient.sendMessage('quit', null);
          }
      });
  
      ipcMain.on('minimize', (evt, arg) => {
          mainWindow.minimize();
      });
      ipcMain.on('maximize', (evt, arg) => {
          mainWindow.isMaximized() ? mainWindow.unmaximize() : mainWindow.maximize();
      });
      ipcMain.on('close', (evt, arg) => {
          mainWindow.close();
      });
      ipcMain.on('opendevtools', (evt, arg) => {
          mainWindow.webContents.openDevTools();
      });
  
      if(IS_DEVELOPMENT === true){
          connectClient = connect.client.create(mainWindow);
          mainWindow.webContents.openDevTools();
      }
  }
  
  
new_contents: 
  import path from 'path';
  import {app, ipcMain, BrowserWindow} from 'electron';
  import connect from 'electron-connect';
  
  // constant variable ==========================================================
  const IS_DEVELOPMENT = __MODE__ === 'development';
  const INDEX_HTML_PATH = IS_DEVELOPMENT ? './app/client/index.html' : './client/index.html';
  const MAIN_WINDOW_PARAMETER = {
      width: 1500,
      height: 800,
      frame: false,
      webPreferences: {
          nodeIntegration: true
      }
  };
  
  // variables ==================================================================
  let mainWindow;    // main window
  let connectClient; // connector from electron-connect for client
  
  // app events =================================================================
  let isLockable = app.requestSingleInstanceLock();
  if(isLockable !== true){app.quit();}
  
  app.on('second-instance', () => {
      if(mainWindow != null){
          if(mainWindow.isMinimized() === true){
              mainWindow.restore();
          }
          mainWindow.focus();
      }
  });
  
  app.on('ready', () => {
      createMainWindow();
  });
  
  app.on('window-all-closed', () => {
      mainWindow = null;
      app.quit();
  });
  
  // function ===================================================================
  function createMainWindow(){
      // create new browser window
      mainWindow = new BrowserWindow(MAIN_WINDOW_PARAMETER);
      mainWindow.loadFile(INDEX_HTML_PATH);
  
      mainWindow.on('closed', () => {
          mainWindow = null;
          if(IS_DEVELOPMENT === true){
              connectClient.sendMessage('quit', null);
          }
      });
  
      ipcMain.on('minimize', (evt, arg) => {
          mainWindow.minimize();
      });
      ipcMain.on('maximize', (evt, arg) => {
          mainWindow.isMaximized() ? mainWindow.unmaximize() : mainWindow.maximize();
      });
      ipcMain.on('close', (evt, arg) => {
          mainWindow.close();
      });
      ipcMain.on('opendevtools', (evt, arg) => {
          mainWindow.webContents.openDevTools();
      });
      ipcMain.on('settitle', (evt, arg) => {
          mainWindow.setTitle(arg);
          evt.sender.send('settitledom', arg);
      });
  
      if(IS_DEVELOPMENT === true){
          connectClient = connect.client.create(mainWindow);
          mainWindow.webContents.openDevTools();
      }
  }
  
  
subject: add settitle method