Fixed heights/content JavaScript applications

gistfile1.txt

(function (root, document, undefined) {

  var $$ = function () {
    return document.querySelectorAll(arguments[0]);
  };

  var header = $$('.header')[0];
  var headerHeight = header.offsetHeight;
  var content = $$('.main')[0];
  var sidebar = $$('.sidebar')[0];

  var resizeContent = function () {
    var height = Math.max(document.documentElement['clientHeight'], document.body['scrollHeight'], document.documentElement['scrollHeight'], document.body['offsetHeight'], document.documentElement['offsetHeight']);
    content.style.height = (height - 45) + 'px';
    sidebar.style.height = (height - 45) + 'px';
  };

  resizeContent();

  root.addEventListener('resize', resizeContent);

})(this, document);

At line 22, what is supposed to be the "this" keyword?
Is it the window object?