下面这段代码有错误吗？为什么在浏览器显示的是空白页面

<script type="text/javascript">
        
           function member(name,gender)
           {
              this.name=name;
              this.gender=gender;
           }
            
           function showproperty(obj,objstring)
           {
              var str="";
              for(var i in obj)
              {
                str+=objString+"."+i+"="+obj[i]+"<br>";
              }
              return str;
           }
         
           person1=new member("zhangsan","男");
            
           person2=new member("lisi","女");
         
           document.write(showproperty(person1,"person"));
           document.write(showproperty(person2,"person"));
         
           
       </script>