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;
}