我的代码哪错了阿

<script language="JavaScript">
  function submitinfor()
  {
   var product_name=new Array(5);
   var order_number=new Array(5);
   var single_price=new Array(5);
   var total_price=new Array(5);
   var date=new Array(5);
   var supplier=new Array(5);
     product_name[1]=document.my.textfield1.value;
     order_number[1]=document.my.textfield2.value;
     single_price[1]=document.my.textfield3.value; 
      total_price[1]=document.my.textfield4.value; 
             date[1]=document.my.textfield5.value; 
         supplier[1]=document.my.textfield6.value;
     product_name[2]=document.my.textfield7.value;
     order_number[2]=document.my.textfield8.value;
     single_price[2]=document.my.textfield9.value; 
      total_price[2]=document.my.textfield10.value; 
             date[2]=document.my.textfield11.value; 
         supplier[2]=document.my.textfield12.value;
     product_name[3]=document.my.textfield13.value;
     order_number[3]=document.my.textfield14.value;
     single_price[3]=document.my.textfield15.value; 
      total_price[3]=document.my.textfield16.value; 
             date[3]=document.my.textfield17.value; 
         supplier[3]=document.my.textfield18.value;
     product_name[4]=document.my.textfield19.value;
     order_number[4]=document.my.textfield20.value;
     single_price[4]=document.my.textfield21.value; 
      total_price[4]=document.my.textfield22.value; 
             date[4]=document.my.textfield23.value; 
         supplier[4]=document.my.textfield24.value;
     product_name[5]=document.my.textfield25.value;
     order_number[5]=document.my.textfield26.value;
     single_price[5]=document.my.textfield27.value; 
      total_price[5]=document.my.textfield28.value; 
             date[5]=document.my.textfield29.value; 
         supplier[5]=document.my.textfield30.value;
  
     alert("asdfasdf");
 }
</script>
my是个表单名字~textfield1是<input type="text" name="textfield1" size=10>
这样~一运行 “document.my.textfield1 ”is null or not a object 为什么啊~