自定义对象 获得对象得个数

Question

<script type="text/javascript" language="javascript">
        function fun(Obj)
        {
            var str="";
            //如果想知道 obj 有哪些成员 
            //写如下代码
            //不知道  是否有属性获得对象长度
            //如 Obj.length等等的属性
            if(Obj.left!=null)
            {
                str+="\nleft:"+Obj.left;
            }else
            {
                str+="\nleft:NULL";
            }
            
            if(Obj.width!=null)
            {
                str+="\nwidth:"+Obj.width;
            }else
            {
                str+="\nwidth:NULL";
            }
            
            if(Obj.top!=null)
            {
                str+="\ntop:"+Obj.top;
            }else
            {
                str+="\ntop:NULL";
            }
            
            alert(str);                        
        }        
        fun({left:"100px",width:"100px"});
    </script>    

Answer 1

for (var obj in xxx)
{
    document.write( xxx[obj] + ", "  + obj );
}