Une fonction bien pratique qui permet de récupérer les variables GET en javascript :

 function getVar(name)
         {
         get_string = document.location.search;
         return_value = '';

         do { //cette boucle va capturer toutes les instances des variables GET.
            name_index = get_string.indexOf(name + '=');

            if(name_index != -1)
              {
              get_string = get_string.substr(name_index + name.length + 1, get_string.length - name_index);

              end_of_value = get_string.indexOf('&');
              if(end_of_value != -1)
                value = get_string.substr(0, end_of_value);
              else
                value = get_string;                

              if(return_value == '' || value == '')
                 return_value += value;
              else
                 return_value += ', ' + value;
              }
            } while(name_index != -1)

         space = return_value.indexOf('+');
         while(space != -1)
              {
              return_value = return_value.substr(0, space) + ' ' +
              return_value.substr(space + 1, return_value.length);

              space = return_value.indexOf('+');
              }

         return(return_value);
         }