getElementsByClassName

var getElementsByClassName = function (className, tag, elm){

　　if (document.getElementsByClassName) {

　　getElementsByClassName = function (className, tag, elm) {

　　elm = elm || document;

　　var elements = elm.getElementsByClassName(className),

　　nodeName = (tag)? new RegExp("\\b" + tag + "\\b", "i") : null,

　　returnElements = [],　current;

　　for(var i=0, il=elements.length; i

　　current = elements[i];

　　if(!nodeName || nodeName.test(current.nodeName)) {

　　returnElements.push(current);}}

　　return returnElements;};}

　　else if (document.evaluate) {getElementsByClassName = function (className, tag, elm) {

　　tag = tag || "*";elm = elm || document;var classes = className.split(" "),classesToCheck = "",

　　xhtmlNamespace = "http://www.w3.org/1999/xhtml",

　　namespaceResolver = (document.documentElement.namespaceURI === xhtmlNamespace)? xhtmlNamespace : null,

　　returnElements = [],elements,node;

　　for(var j=0, jl=classes.length; j

　　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);}

　　while ((node = elements.iterateNext())) {

　　returnElements.push(node);}return returnElements;};}

　　else {getElementsByClassName = function (className, tag, elm) {

　　tag = tag || "*";elm = elm || document;var classes = className.split(" "),classesToCheck = [],

　　elements = (tag === "*" && elm.all)? elm.all : elm.getElementsByTagName(tag),current,returnElements = [],match;

　　for(var k=0, kl=classes.length; k<KL; k+="1){classesToCheck.push(new" regexp(?(^|\\s)?="" classes[k]="" +="" ?(\\s|$)?));}<="" p="">

　　for(var l=0, ll=elements.length; l

　　for(var m=0, ml=classesToCheck.length; m

　　match = classesToCheck[m].test(current.className);

　　if (!match) {break;}}

　　if (match) {returnElements.push(current);　}}return returnElements;};}

　　return getElementsByClassName(className, tag, elm);};