jQuery(document).ready(function() {
    jQuery("#field_id")
    .autocomplete('/frontend_dev.php/module/ajax', jQuery.extend({}, {
      dataType: 'json',
      parse:    function(data) {
        var parsed = [];
        for (key in data) {
          parsed[parsed.length] = { data: [ data[key], key ], value: data[key], result: data[key] };
        }
        return parsed;
      }
    }, { }))
    .result(function(event, data) { jQuery("#field_id").val(data[1]); });
  });