code: function() {
        var self = this,
            val = $.map(self.items(), function(item) {
              return self.options.itemValue(item).toString();
            });
  
        self.$element.val(val, true);
  
        if (self.options.triggerChange)
          self.$element.trigger('change');
      }
docs: Assembly value by retrieving the value of each item, and set it on the
  element.