var?nav?=?document.getElementById('topNav');
var?lis?=?nav.getElementsByTagName('li');
var?current;
for?(var?i=0;i<lis.length;i++)?{
??if?((/\b(current)\b/).test(lis.className))?{
???current?=?lis[i];
???break;
?}
}
for?(var?i=0;i<lis.length;i++)?{
??lis[i].mouseenter?=?function?()?{
??	current.className?=?'';
??	current?=?this;
????this.className?=?'current';
??}
}

怎么感覺有點小錯誤，你先試一下吧

?var?load?=?function(){
????????var?lis?=?document.getElementsByTagName("li"),
????????i=0,
????????liLength?=?lis.length,
????????current;
????????for(;i<liLength;i++){
??????????(function(k){
????????????lis[i].onclick?=?function(){
?????????????if(current){
??????????????current.className?=?"";
????????????}
????????????this.className?=?"current";
????????????current?=?this;
??????????};
????????})(i);
??????}
????};

jQuery還是原生？

$("li").mouseover(function(){
		$(this).addClass("current");
	}).mouseout(function(){
		$(this).removeClass("current");
	})