wrote a program using javascript for showing error message beside field instead of alerting but it is not working please help me to work the program
AlaskasWorld
<html>
   <head>
      <link rel="stylesheet" type="text/css" href="mystyle.css">
      <script type="text/javascript">
         function check()
         {
              if(document.getElementById('firstname').value==NULL || myform.firstname.value.length==0)
              {
                  document.getElementById('errorname').value="this is an invalid name";
              }
         }
      </script>
   </head>
   <body>
      <form name="myform">
         <p>name</p>
         <input type="text" name="firstname" onblur="check()"/>
         <span id="errorname"></span>
         <br/><input type="button" value="submit" />
      </form>
   </body>
</html>