JS根据class获取元素的方法

function getByClass(oParent, sClass){
    var aResult=[];
    var aEle=oParent.getElementsByTagName('*');
    for(var i=0;i<aEle.length;i++){
        if(aEle[i].className==sClass)
        {
            aResult.push(aEle[i]);
        }
    }
    return aResult;
}

用法如下

window.onload=function (){
    var oUl=document.getElementById('ul1');
    var aBox=getByClass(oUl, 'box');
    for(var i=0;i<aBox.length;i++){
        aBox[i].style.background='red';
    }
};

解决IE8以下不支持getElementsByClassName的方法

//解决IE8之类不支持getElementsByClassName
if (!document.getElementsByClassName) {
    document.getElementsByClassName = function (className, element) {
        var children = (element || document).getElementsByTagName('*');
        var elements = new Array();
        for (var i = 0; i < children.length; i++) {
            var child = children[i];
            var classNames = child.className.split(' ');
            for (var j = 0; j < classNames.length; j++) {
                if (classNames[j] == className) {
                    elements.push(child);
                    break;
                }
            }
        }
        return elements;
    };
}