how to install electron JS ?

{
  "name": "myapp",
  "version": "0.1.0",
  "main": "index.js",
  "scripts": {
    "start": "electron ."
  },
  "author": "Mitul Dabhi <dabhi.mitul.developer@gmail.com> (http://gmail.com)",
  "license": "MIT",
  "devDependencies": {
    "electron-packager": "^8.6.0",
    "electron-prebuilt": "^0.25.3"
  },
  "description": ""
}

npm i electron-prebuilt --save-dev

 var app = require('app');
var browserWindow = require('browser-window');
app.on('ready',function(){
 var mainWindow = new browserWindow({
 width : 800 , height : 600
 });
});

npm start

npm install electron -g