i got an error when runing the tutorials

I get this error when i run electron app.js but when i run electron index.html everything works fine
i got this in my app.js file

var electron = require('electron')

electron.app.on('ready', function () {
  var mainWindow = new electron.BrowserWindow({width: 600, height: 800})
  mainWindow.loadURL('file://' + __dirname + '/index.html')
})

App threw an error when running

[TypeError: Cannot read property 'on' of undefined]
A JavaScript error occurred in the main process
Uncaught Exception:
TypeError: Cannot read property 'on' of undefined
    at Object.<anonymous> (/home/jose/electron/app.js:3:13)
    at Module._compile (module.js:425:26)
    at Object.Module._extensions..js (module.js:432:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:313:12)
    at loadApplicationPackage (/usr/local/lib/node_modules/electron-prebuilt/dist/resources/default_app/main.js:257:23)
    at Object.<anonymous> (/usr/local/lib/node_modules/electron-prebuilt/dist/resources/default_app/main.js:289:5)
    at Module._compile (module.js:425:26)
    at Object.Module._extensions..js (module.js:432:10)
    at Module.load (module.js:356:32)

Start with app.js and reproduce the failure using electron app.js; compare that entry point with the working electron index.html command and the Electron API used in the tutorial. Done means the tutorial's app.js command runs without the reported exception and loads index.html as intended.