Simple polyfill for fetching all elements on the page with the given class

getElementsByClassName.min.js

"getElementsByClassName"in document||(document.getElementsByClassName=document.evaluate?function(a){var a="[contains(concat(' ', @class, ' '), ' "+a+" ')]",d="http://www.w3.org/1999/xhtml"===document.documentElement.namespaceURI?"http://www.w3.org/1999/xhtml":null,b;try{b=document.evaluate(".//*"+a,document,d,0,null)}catch(c){b=document.evaluate(".//*"+a,document,null,0,null)}return b}:function(a){for(var a=RegExp("(^|\\s)"+a+"(\\s|$)"),d=document.all||document.getElementsByTagName("*"),b=[],c=0,e=
d.length;c<e;c+=1)a.test(d[c].className)&&b.push(d[c]);return b});

simpleGetElementsByClassName.js

/*
  Based on "The ultimate getElementsByClassName, anno 2008" by Robert Nyman
  http://robertnyman.com/2008/05/27/the-ultimate-getelementsbyclassname-anno-2008/
  Developed by Jon Gjengset <jon@thesquareplanet.com>
  MIT license

  This file will provide a stupidly simple fallback for getElementByClassName
  Namely one that only supports lookup of a single class, and only on document
  It also won't allow limiting results to only tags of a single type
  Also, return types won't be normalized, so you might get an array or a NodeList depending
  on the underlying implementation being used.

  It is also about half the size of the Ultimate version at 1.8KB (571B minified) vs 2.4KB (1.05KB minified)
*/
if (!("getElementsByClassName" in document)) {
  if (document.evaluate) {
    document.getElementsByClassName = function (className) {
      var classCheck = "[contains(concat(' ', @class, ' '), ' " + className + " ')]",
        xhtmlNamespace = "http://www.w3.org/1999/xhtml",
        namespaceResolver = (document.documentElement.namespaceURI === xhtmlNamespace)? xhtmlNamespace : null,
        elements;
      try {
        elements = document.evaluate(".//*" + classCheck, document, namespaceResolver, 0, null);
      }
      catch (e) {
        elements = document.evaluate(".//*" + classCheck, document, null, 0, null);
      }

      return elements;
    };
  } else {
    document.getElementsByClassName = function (className) {
      var classCheck = new RegExp("(^|\\s)" + className + "(\\s|$)"),
        elements = document.all || document.getElementsByTagName('*'),
        returnElements = [];

      for (var l=0, ll=elements.length; l<ll; l+=1) {
        if (classCheck.test(elements[l].className)) {
          returnElements.push(elements[l]);
        }
      }

      return returnElements;
    }
  }
}