怎么提示abc是未定义对象
<html>  
        <head>  
           <title>  
          information 
           </title>  
        </head>      
  <script   language=JavaScript>  
 function   show() 
 { 
       window.alert( "this.info ");   
 }   
 function   myInformation(a,b,c) 
 {   this.pro=a; 
       this.city=b; 
       this.road=c; 
       this.info= "地址是 "+this.pro+this.city+this.road; 
       this.show=show; 
 }   
 var   abc=new   myInformation( "安徽省 ", "合肥市 ", "人民路 ");   
  </script>  
  <body>    
  <form>  
  <input   type= "button "   value= "我的地址显示 "   onclick=abc.show() ">  
  </form>    
  </body>  
  </html>  
------解决方案--------------------函数的参数不用定义参数类型吗?
------解决方案-------------------- <html>  
    <head>  
     <title>  
    information 
     </title>  
    </head>      
  <script language=JavaScript>  
 function show() 
 { 
   window.alert(this.info);  //为什么要加引号?   
 }   
 function myInformation(a,b,c) 
 { this.pro=a; 
   this.city=b; 
   this.road=c; 
   this.info= "地址是 "+this.pro+this.city+this.road; 
   this.show=show; 
 }   
 var abc=new myInformation( "安徽省 ", "合肥市 ", "人民路 "); //发现中文逗号   
  </script>  
  <body>    
  <form>  
  <input type= "button " value= "我的地址显示 " onclick= "abc.show() ">  //少了一个双引号, 
  </form>    
  </body>  
  </html>    
------解决方案--------------------如果是null就是未定以