这个javascript为什么又能赋过去this呢

[code="java"]
function invoice(st,ed,len){
var spd=20;
var ul=document.getElementById('invoiceing');
var dv=ul.parentNode;
this.show=function (){
ul.innerHTML='';
ul.previousSibling.innerHTML='入票中......';
dv.style.display='block';
dv.style.height=document.body.clientHeight;
dv.style.width=document.body.clientWidth;
}
this.stop=function (){
window.clearInterval(this.running);
ul.previousSibling.innerHTML='返回';
ul.previousSibling.firstChild.onclick=this.hide;
}
this.hide=function(){
dv.style.height='0px';
dv.style.width='0px';
dv.style.display='none';
}
this.rupiao=function(){
var p=this;
return function(){
var li=document.createElement('

');
li.innerHTML=p.lpad();
ul.appendChild(li);
if(st++>=ed)p.stop();
}
}
this.lpad=function (){
var snum=st.toString();
while(snum.length<len)snum='0'+snum;
return snum;
}
this.doing=function(){
this.show();
var fun=this.rupiao();
this.running=window.setInterval(fun,spd);
}
this.doing.apply(this);
}
[/code]
请问刚才给我解答问题的朋友 这里的hide函数为什么能接到this对象呢 怎么解释呢

this.stop=function (){   
    window.clearInterval(this.running);   
    ul.previousSibling.innerHTML='<a href="javascript:;">返回</a>';   
    ul.previousSibling.firstChild.onclick=this.hide;   
}   

//关键的问题在于this.hide这个函数里有没有引用this，刚刚可能你没理解清楚我说的，
this.hide=function(){

dv.style.height='0px';

dv.style.width='0px';

dv.style.display='none';

}

之前那个版本的hide里面引用了this，
hide:function(){

this.dv.style.height='0px';

this.dv.style.width='0px';

this.dv.style.display='none';

},

其实ul.previousSibling.firstChild.onclick=this.hide;相当于

ul.previousSibling.firstChild.onclick=function(){

this.dv.style.height='0px';

this.dv.style.width='0px';

this.dv.style.display='none';

};