这js代码 求解释 感觉脑容量不够了。。。。。。。麻烦说明一下脉络和变量取值 非常感谢！！！
window.onload=function(){
var aLi=document.getElementsByTagName('li');
for(var i=0; i<aLi.length; i++){
aLi[i].onmouseover=function(){
var oSubNav=this.getElementsByTagName('ul')[0];
if(oSubNav){
var This=oSubNav;
clearInterval(This.time);
This.time=setInterval(function(){
This.style.height=This.offsetHeight+16+"px";
if(This.offsetHeight>=120)
clearInterval(This.time);
},30)
}
}
//鼠标离开菜单，二级菜单动画收缩起来。
aLi[i].onmouseout=function(){
var oSubNav=this.getElementsByTagName('ul')[0];
if(oSubNav){
var This=oSubNav;
clearInterval(This.time);
This.time=setInterval(function(){
This.style.height=This.offsetHeight-16+"px";
if(This.offsetHeight<=0)
clearInterval(This.time);
},30)
}
}
}
}
