getElementsByClassName

/**
 *   Original code developed by Robert Nyman, http://www.robertnyman.com
 *   Code/licensing: http://code.google.com/p/getelementsbyclassname/
 *
 *   Arcnovus modifications:
 *   - Tweaked code to pass JSLint validation (all vars declared together, no more assignment in expressions).
 *   - Added 'item' method to array returned in order to mimick nodeList
 */
(function (window, document) {
    'use strict';

    document.getElementsByClassName = function (className, tag, elm) {
        var i, il, j, jl, k, kl, l, ll, m, ml,
            elements, nodeName, returnElements, current,
            classes, classesToCheck, xhtmlNamespace, namespaceResolver, node,
            match;

        returnElements = [];

        /**
         * This method mimicks the 'item' method of a NodeList object.
         * Adding it here prevents code that expects getElementsByClassName
         * to return a nodelist from potentially breaking.
         * param: idx {Number} index of item to return
         */
        returnElements.item = function (idx) {
            return this[idx];
        };

        if (document.getElementsByClassName) {
            document.getElementsByClassName = function (className, tag, elm) {
                elm = elm || document;
                elements = elm.getElementsByClassName(className);
                nodeName = (tag) ? new RegExp("\\b" + tag + "\\b", "i") : null;

                for (i = 0, il = elements.length; i < il; i += 1) {
                    current = elements[i];
                    if (!nodeName || nodeName.test(current.nodeName)) {
                        returnElements.push(current);
                    }
                }
                return returnElements;
            };
        } else if (document.evaluate) {
            document.getElementsByClassName = function (className, tag, elm) {
                tag = tag || "*";
                elm = elm || document;
                classes = className.split(" ");
                classesToCheck = "";
                xhtmlNamespace = "http://www.w3.org/1999/xhtml";
                namespaceResolver = (document.documentElement.namespaceURI === xhtmlNamespace) ? xhtmlNamespace : null;


                for (j = 0, jl = classes.length; j < jl; j += 1) {
                    classesToCheck += "[contains(concat(' ', @class, ' '), ' " + classes[j] + " ')]";
                }
                try {
                    elements = document.evaluate(".//" + tag + classesToCheck, elm, namespaceResolver, 0, null);
                } catch (e) {
                    elements = document.evaluate(".//" + tag + classesToCheck, elm, null, 0, null);
                }
                do {
                    node = elements.iterateNext();
                    returnElements.push(node);
                } while (node);
                return returnElements;
            };
        } else {
            document.getElementsByClassName = function (className, tag, elm) {
                tag = tag || "*";
                elm = elm || document;
                classes = className.split(" ");
                classesToCheck = [];
                elements = (tag === "*" && elm.all) ? elm.all : elm.getElementsByTagName(tag);


                for (k = 0, kl = classes.length; k < kl; k += 1) {
                    classesToCheck.push(new RegExp("(^|\\s)" + classes[k] + "(\\s|$)"));
                }
                for (l = 0, ll = elements.length; l < ll; l += 1) {
                    current = elements[l];
                    match = false;
                    for (m = 0, ml = classesToCheck.length; m < ml; m += 1) {
                        match = classesToCheck[m].test(current.className);
                        if (!match) {
                            break;
                        }
                    }
                    if (match) {
                        returnElements.push(current);
                    }
                }
                return returnElements;
            };
        }
        return document.getElementsByClassName(className, tag, elm);
    };

}(this, this.document));