Javascript substring function is not working while replace() function is working

[Lei]

 

  <script language="javascript" type="text/javascript">

     $(document).ready(function () {

        var row= $("#testing1").text().substring(2);

        alert(row);

     });

 </script>

the above code isn't working while the following one is good:

 <script language="javascript" type="text/javascript">

     $(document).ready(function () {

        var row= $("#testing1").text().replace("MCV:",'');

        alert(row);

     });

 </script>