document.getElementsByClassName 的理想实现

//三个参数都是必需的，查找一网页中5007个类名为“cell”的元素，IE8历时1828 ~ 1844毫秒，
//IE6为4610 ~ 6109毫秒，FF3.5为46 ~ 48毫秒，opera10为31 ~ 32毫秒，Chrome为23~ 26毫秒，
//safari4为19 ~ 20毫秒

function getElementsByClassName(oElm,strTagName,strClassName){//使用document.getElementsByTagName(*)获取所有的元素，然后进行遍历.为了兼容IE5，加document.all分支判断var arrElements=(strTagName=="*"&&oElem.all)?oElem.all:oElem.getElementsByTagName(strTagName);//进行遍历，使用正则表达式找出匹配的元素放入一个数组返回var arrReturnElements=new Array();strClassName=strClassName.replace(/\-/g,'\\-');var oRegExp=new RegExp('(^|\\s)'+strClassName+'(\\s|$)');var oElement;for(var i=0;i<arrElements.length;i++){oElement=arrElements[i];if(oRegExp.test(oElement.className)){arrReturnElements.push(oElement);}}return (arrReturnElements);};

//后两参数是可靠的，查找一网页中5007个类名为“cell”的元素，IE8历时78毫秒，IE6历时125~171毫秒
//FF3.5为42 ~ 48毫秒，opera10为31 毫秒，Chrome为22~ 25毫秒，safari4为18 ~ 19毫秒

function getElementsByClassName(searchClass,node,tag){var classElements=new Array();if(node==null){node=document;}if(tag==null){tag='*';}var els=node.getElementsByTagName(tag);var elsLen=els.length;var pattern=new RegExp('(^|//s)',searchClass,'(//s|$)');for(var i=0,j=0;i<elsLen;i++){if(pattern.test(els[i].className)){classElements[j]=els[i];j++;}}return classElements;}

//由于这是后期添加的，测试页面已被我删掉，没有做测试……

function getElementsByClassName(className,element){var children=(element||document).getElementsByTagName('*');var elements=new Array();for(var i=0;i<children.lenght;i++){var child=children[i];var classNames=child.className.split(' ');for(var j=0;j<classNames;j++){if(classNames[j]==className){elements.push(child);break;}}}return elements;};

//查找一网页中5007个类名为“cell”的元素，FF3.5为104 ~ 
119毫秒，opera10为230 ~ 265毫秒，//Chrome为119 ~ 128毫秒，safari为28 ~ 32毫秒

var getElementsByClassName = function(searchClass) {function acceptNode(node) {if (node.hasAttribute("class")) {var c = " " + node.className + " ";if (c.indexOf(" " + searchClass + " ") != -1)return NodeFilter.FILTER_ACCEPT;}return NodeFilter.FILTER_SKIP;}var treeWalker = document.createTreeWalker(document.documentElement,NodeFilter.SHOW_ELEMENT, acceptNode, true);var returnElements = [];if (treeWalker) {var node = treeWalker.nextNode();while (node) {returnElements.push(node);node = treeWalker.nextNode();}}return returnElements;
}

document.getElementsByClassName = function(className, parentElement) {if (Prototype.BrowserFeatures.XPath) {var q = ".//*[contains(concat(' ', @class, ' '), ' " + className + " ')]";return document._getElementsByXPath(q, parentElement);} else {var children = ($(parentElement) || document.body).getElementsByTagName('*');var elements = [], child;for (var i = 0, length = children.length; i < length; i++) {child = children[i];if (Element.hasClassName(child, className))elements.push(Element.extend(child));}return elements;}
};

//查找一网页中5007个类名为“cell”的元素，FF3.5为33 ~ 48毫秒，opera10为31 ~ 32毫秒，
//Chrome为104 ~ 107毫秒，safari为18 ~ 21毫秒

function getElementsByClassName(searchClass,node,tag){node=node||document;tag=tag||'*';var classes=searchClass.split(' '),patterns="",xhtmlNamespace='http://www.w3c.org/1999/xhtml',namespaceResolver=(document.documentElement.namespaceURI===xhtmlNamespace)?xhtmlNamespace:null,returnElements=[],elements,_node;for(var j=0,jl=classes.length;j<jl;j++){patterns+="[contains(concat(' ',@class,' '),' "+classes[j]+" ')]";}try{elements=document.evaluate('.//'+tag+patterns,node,namespaceResolver,0,null);}catch(e){elements=document.evaluate('.//'+tag+patterns,node,null,0,null);}while((_node=elements.iterateNext())){returnElements.push(node);}return returnElements;};

//查找一网页中5007个类名为“cell”的元素，IE8历时1828 ~ 1844毫秒，
//IE6为125 ~ 172毫秒，IE8为93 ~ 94毫秒，FF3.5为0~1毫秒，opera10为0毫秒，Chrome为1毫秒，
//safari4为0毫秒

function getElementsByClassName(searchClass,node,tag){if(document.getElementsByClassName){return document.getElementsByClassName(searchClass);}else{node=node||document;tag=tag||"*";var returnElements=[];var els=(tag=='*'&&node.all)?node.all:node.getElementsByTagName(tag);var i=els.length;searchClass=searchClass.replace(/\-/g,'\\-');var pattern=new RegExp('(^|\\s)'+searchClass+'(\\s|$)');while(--i>=0){if(pattern.test(els[i].className)){returnElements.push(els[i]);}}return returnElements;}};

var collections = getElementsByClassName("red");

<h2 class="red cell title">安装支持</h2> 
<span class="cell red ">jjj</span> 
<div class="filament_table red cell">这是DIV</div> 
#利用 var dd = getElementsByClassName("cell red") ，这三个元素都应该能被检索到！

function getElementsByClassName(searchClass,node,tag){if(document.getElementsByClassName){return document.getElementsByClassName(searchClass);}else{node=node||document;tag=tag||"*";var classes=searchClass.split(" "),elements=(tag=='*'&&node.all)?node.all:node.getElementsByTagName(tag),patterns=[],returnElements=[],current,match;var i=classes.length;while(--i>=0){patterns.push(new RegExp('(^|\\s)'+ classes[i] +'(\\s|$)'));}var j=elements.length;while(--j>=0){current=elements[j];match=false;for(var k=0,kl=patterns.length;k<kl;k++){match=patterns[k].test(current.className);if(!match){break;}if(match){return returnElements.push(current);}}				}return returnElements;}};