Small snippet to detect global variables.

globalVariables.js

(function (global) {
  'use strict';
  
  var globals = [];
  var iframe = document.createElement('iframe');
  var cleanWindow;
  
  iframe.src = 'about:blank';
  iframe.style.display = 'none';
  document.body.appendChild(iframe);
  
  cleanWindow = Object.assign({}, iframe.contentWindow, iframe.contentDocument);
  iframe.parentNode.removeChild(iframe);
  globals = Object.keys(global)
    .map(function (key) { if (!(key in cleanWindow) ) { return key; } })
    .filter(function (val) { return !!val; })
    .sort();

  console.log(globals.length, globals);
}(this));