js: getDocHeight(), Get document height (cross-browser)

Utility.js

  // Get document height (cross-browser)
  // 
  // This function will return any document’s height. It’s been tested in IE6/7, 
  // FF2/3, Safari (Windows), Google Chrome and Opera 9.5. If the actual document’s
  // body height is less than the viewport height then it will return the viewport 
  // height instead.
  // 
  // @return {number}
  function getDocHeight() {
    var D = document;
    return Math.max(
        Math.max(D.body.scrollHeight, D.documentElement.scrollHeight),
        Math.max(D.body.offsetHeight, D.documentElement.offsetHeight),
        Math.max(D.body.clientHeight, D.documentElement.clientHeight)
    );
  }

Why do you call Math.max four times? You need the outer one.