getElementsByClassName polyfill

getElementsByClassNamePolyfill.js

/*jshint forin:true, noarg:true, noempty:true, eqeqeq:true, bitwise:true, strict:true, undef:true, curly:true, browser:true, indent:2, maxerr:50 */
(function (document) {
  "use strict";
  if (!document.getElementsByClassName) {
    document.getElementsByClassName = function (match) {
      var result = [],
        elements = document.body.getElementsByTagName('*'),
        i, elem;
      match = " " + match + " ";
      for (i = 0; i < elements.length; i++) {
        elem = elements[i];
        if ((" " + (elem.className || elem.getAttribute("class")) + " ").indexOf(match) > -1) {
          result.push(elem);
        }
      }
      return result;
    };
  }
}(document));

Couple improvements:

• Run the polyfill when the function is not found on the document
• Only get tags that are children of the body, rather than getting all tags in the document, since only the body and its children should have classnames (tradeoff here is this doesn't include the body element itself, but I'm ok with that)