js切换换class

1，

function ntabs(thisObj,Num)
            {if(thisObj.className == "active")return;
            var tabObj = thisObj.parentNode.id;
            var tabList = document.getElementById(tabObj).getElementsByTagName("li");
            for(i=0; i <tabList.length; i++)
                {if (i == Num)
                    {thisObj.className = "active";
                    document.getElementById(tabObj+"_cont"+i).style.display = "block";
                    }
                    else{
                        tabList[i].className = "normal";
                        document.getElementById(tabObj+"_cont"+i).style.display = "none";
                }
            }
        }

2，
$(document).ready(function(){

    var $tab_li = $('.tab ul li');

    $tab_li.hover(function(){

        $(this).addClass('selected').siblings().removeClass('selected');

        var index = $tab_li.index(this);

        $('div.tab_box > div').eq(index).show().siblings().hide();

    });

});