basic jquery script not working

basic jquery script not working

im trying to make a script so that if a user selects a county ie. 'United Kingdom' then it will show Postcode in a input field but form some reason im getting no joy...can anyone give me advise on this please...thank you

  1. $(document).ready(function()
    {
          var locator           = $("#locator"),
              location_selected = $("#location option:selected").text();

              if (location_selected == 'United Kingdom')
              {
                    locator.val('Postcode');
                      locator.addClass('locator-pattern');
              }
              else if (location_selected == 'Saudi Arabia')
              {
                  locator.val('PO Box, Region');
                  locator.addClass('locator-pattern');
              }

              locator.focus(function()
              {
                  var locator_value = locator.val();

                    if (locator_value == 'Postcode' || locator_value == 'PO Box, Region')
                    {   
                      locator.val('');
                      locator.addClass('locator');
                    }
              });    
    });