function $(id){

return typeof id==='string'?document.getElementById(id):id;

}

window.onload=function(){

//获取鼠标滑过或点击的标签和要切换内容的元素

    var titles=$('notice-tit').getElementsByTagName('li'),

    divs=$('notice-con').getElementsByTagName('div');

    alert(titles.length);

}