AngularJS - Add any directive dynamically

<!doctype html>
<html ng-app="plunker">

<head>
    <script src="http://code.angularjs.org/1.2.20/angular.js"></script>
    <script src="http://angular-ui.github.io/bootstrap/ui-bootstrap-tpls-0.6.0.js"></script>
    <script src="example.js"></script>
    <link href="//netdna.bootstrapcdn.com/twitter-bootstrap/2.3.1/css/bootstrap-combined.min.css" rel="stylesheet">
</head>

<body>

    <div data-ng-controller="DatepickerDemoCtrl">

        <select data-ng-options="s for s in selects" data-ng-model="el" 
            data-dynamic-directives="[
                { 'if' : 'selectIsRequired', 'ng-required' : '{{selectIsRequired}}' },
                { 'tooltip-placement' : 'bottom' },
                { 'if' : 'addTooltip()', 'tooltip' : '{{ dt() }}' }
            ]">
            <option value=""></option>
        </select>

    </div>
</body>

</html>

angular.module('plunker', ['ui.bootstrap'])
    .controller('DatepickerDemoCtrl', ['$scope',
        function($scope) {
            $scope.dt = function() {
                return new Date();
            };
            $scope.selects = [1, 2, 3, 4];
            $scope.el = 2;

            // For use with our dynamic-directive
            $scope.selectIsRequired = true;
            $scope.addTooltip = function() {
                return true;
            };
        }
    ])
    .directive('dynamicDirectives', ['$compile',
        function($compile) {
            
             var addDirectiveToElement = function(scope, element, dir) {
                var propName;
                if (dir.if) {
                    propName = Object.keys(dir)[1];
                    var addDirective = scope.$eval(dir.if);
                    if (addDirective) {
                        element.attr(propName, dir[propName]);
                    }
                } else { // No condition, just add directive
                    propName = Object.keys(dir)[0];
                    element.attr(propName, dir[propName]);
                }
            };
            
            var linker = function(scope, element, attrs) {
                var directives = scope.$eval(attrs.dynamicDirectives);
        
                if (!directives || !angular.isArray(directives)) {
                    return $compile(element)(scope);
                }
               
                // Add all directives in the array
                angular.forEach(directives, function(dir){
                    addDirectiveToElement(scope, element, dir);
                });
                
                // Remove attribute used to add this directive
                element.removeAttr(attrs.$attr.dynamicDirectives);
                // Compile element to run other directives
                $compile(element)(scope);
            };
        
            return {
                priority: 1000, // Run before other directives,
                terminal: true, // Stop other directives running
                link: linker
            };
        }
    ]);