function addClass(obj,className){
?obj.className+=" "+className;
?return obj;?
}

?

?

function removeClass(obj,className){
?var s=obj.className.split(/\s+/);//使用空格为分隔符，把class连成数组
?for(var i=0;i<s.length;i++){
??if(s[i]==className){delete s[i];}??
?}?
?obj.className=s.join(" ");//把数组元素用空格链接后重新赋值给className
?return obj;?
}