javascript 内存回收机制理解

<script>
function aa(){
this.rr = "弹窗";
}
function bb(){
this.rr = "弹窗";
}
var b1;
function cc(){
var a1 = new aa();
b1 = new bb();
return b1;
}
cc();
alert(b1.rr)
</script>

<script>
function aa(){
this.rr = "弹窗";
}
function bb(){
this.rr = "弹窗";
}
function cc(){
var a1 = new aa();
var b1 = new bb();
return b1;
}
var b1 = cc();
alert(b1.rr);
</script>

<SCRIPT LANGUAGE="JavaScript">
<!--
//猫
function cat(name){
var zhuren ;
this.name = name;
//设置主人
this.addZhuRen = function(zr){
zhuren = zr;
}
this.getZhuRen = function(){
return zhuren;
}
}
//主人
function zhuren(name){
this.name = name;
}
//创建主人:
var zr = new zhuren("zhangsan");
//创建猫
var cat1 = new cat("asan");
//设置该猫的主人
cat1.addZhuRen(zr);
//释放主人
zr = null ;
//此处还存在对主人对象的引用
alert(cat1.getZhuRen().name)
//-->
</SCRIPT>