dz.ui-select.null-option.js

/**
 * Null-option directive for angular-ui/ui-select.
 *
 * Author: Daniel Zimmermann (Github: dlukez)
 * Version: 0.1
 * License: MIT
 * URL: https://gist.github.com/dlukez/76ea5f42507ba2d810e5
 * Usage/demo: http://plnkr.co/edit/hogYX0loQTb57Pw6RKe7
 */
angular.module('dz.ui-select.null-option', []).directive('nullOption', function () {
    var directive = {
        restrict: 'A',
        require: ['^uiSelect', '^ngModel'],
        link: {
            pre: function ($scope, $element, $attrs, controllers) {
                // treat undefined and null as the same?
                var isNull = angular.isDefined($attrs.looseNull) ?
                                function (value) { return value == null; } :
                                function (value) { return value === null; };

                // get the controllers
                var $select = controllers[0];
                var ngModel = controllers[1];

                // get the null option
                var nullOption = $scope.$eval($attrs[directive.name]);

                // we are going to turn the items property on the $select
                // controller into a getter/setter, in order to add the
                // null option if it isn't already present in the source
                // items list
                var items;
                Object.defineProperty($select, 'items', {
                    get: function () {
                        return items;
                    },
                    set: function (value) {
                        if (value.indexOf(nullOption) === -1) {
                            value.unshift(nullOption);
                        }

                        items = value;
                    }
                });

                // add a parser to convert the null option
                // into an actual null value when it is selected
                // (this should run after $select's parser)
                ngModel.$parsers.push(function (value) {
                    return value === nullOption ? null : value;
                });

                // add a formatter to convert a null value
                // into the null option when the model is set
                // (this should run before $select's formatter)
                ngModel.$formatters.unshift(function (value) {
                    return isNull(value) ? nullOption : value;
                });
            }
        }
    };

    return directive;
});