initSelection for preselected select2 value

select2_config.js

initSelection: function(element, callback) {

            var id=$(element).val();
            if (id!=="") {
                $.ajax("/countries/"+id+".json", {
                    dataType: "json"
                }).done(function(data) {
                    var selected = {id: element.val(), text: data.name + " (" + data.country_code + ")"};
                    callback(selected);
                });
            }
        }