Find out global variables added by scripts on a website

by-iframe.js

/*
  Method1: Create an iframe and compare it's window object with website's window
*/
const iframe = document.createElement('iframe');
document.body.append(iframe);
const virgin = Object.keys(iframe.contentWindow);
const current = Object.keys(window);
const added = current.filter(key => !virgin.includes(key));

by-new-window.js

/*
  Method2: By creating a new window and comparing it's window object with our current window
*/

const newWindow = window.open();
const added = Object.keys(newWindow).filter(key => !newWindow.hasOwnProperty(key));