获取XHTML页面上所有具有相同className的Element对象的javascript函数：

/**
* rootNode          the root node to be checked on,
*                   for example 'document'
* classToSearch     className to be matched
* tagName           elements name to be searched between,
*                   '*' for all elements in 'rootNode'
* returns           an array contains all elements matched
*/
function getElementsByClass(rootNode,classToSearch,tagName) {
    var elementsToReturn = new Array();

    var elementList = rootNode.getElementsByTagName(tagName);
    var nLen = elementList.length;

    var pattern = new RegExp("\\b"+classToSearch+"\\b");

    for(var i = 0; i < nLen; i++){
        if( pattern.test(elementList[i].className) ){
            elementsToReturn[elementsToReturn.length] = elementList[i];
        }
    }
    return elementsToReturn;
}