coo.js

// get an array of all the keys on the window
const dirty = Object.keys(window);

// Then create an iframe set to nothing
const iframe = document.createElement('iframe');
iframe.src = '';

// put it into the DOM
document.body.append(iframe);

// grab an array of the clean iframe's window
const clean = Object.keys(iframe.contentWindow);

// filter the difference
const difference = dirty.filter(prop => !clean.includes(prop));

console.log(difference);