js javascript 根据类名称查找所有元素

function getElementsByClassName(fatherId, tagName, classNames){
    var node = fatherId && document.getElementById(fatherId) || document;
    classNames = classNames.split(" ");
    var elements = node.getElementsByTagName(tagName);
    var result = [];
    for(var i=0,j=elements.length,k=0; i<j; i++){
        var element = elements[i];
        if (element.className == "") continue;
        for (var index in classNames)
        {
            if (classNames[index] == element.className)
            {
                result[k++] = element;
                continue;
            }
        }
    }
    return result;
}