I'm simply trying to set a value for an input but it doesn't work. Here is my jquery function :

  function display_form() 
        {   try {
            $('#start_date').val('2012/08/21');
            }catch (e){
                         alert('error');
                     }

           window.alert( $('[name=start_date]').val() ); 
                      }

This shows "undefined". Here is my form :

<input id="start_date" name="start_date" type="text" size="6" />

Should I put somewhere the id of the form that I want to use? I just followed what is said in the documentation of jquery but it doesn't seem to work. Could anyone help me ?