哪错了．．．．解决办法

哪错了．．．．
var   f=document.form1;
  var   usrName=f.userName.value;

  用户名: <input   type= "text "   id= "userName "   name= "userName "   value= " ">
提示userName为空或不是对像...

[解决办法]
那你输入个值再试试看
或var usrName=document.GetElemengById( "userName ").value;
[解决办法]
var usrName=document.getElementById( "userName ");
alert(usrName.value);
[解决办法]
通过document.GetElemengById( "userName ").Value来获取值
[解决办法]
var f=document.form1( "userName ");
alert(f.value );