Find the new global variable.

glovar

(function() {
  
  // save global scope
  var scope = [];
  for(var p in window) {
    scope.push(p);
  }

  // code
  window.a = 1;

  // check global scope
  // find the new global variable
  for(var property in window) {
    if (scope.indexOf(property) === -1) {
      console.log('Found ' + property);
    }
  }

})();