select_towns.js

function select_towns(towns_string) {
  var towns_arr = towns_string.split(','),
      options = $$('#search_town_data option');
  towns_arr.each(function(town_id_string) {
    options.select(function(opt) {
      return opt.value.match(town_id_string);
    }).invoke('writeAttribute','selected',true);
  });
}