AngularJS module for executing an expression when an element is shown

gistfile1.txt

angular.module('OnShow', []).
    directive('onShow', function () {
        return {
            controller: function($scope) {
                $scope.fireOnce = false;
                this.setFireOnce = function(bool) {
                    $scope.fireOnce = bool;
                }
            },
            link: function(scope, elm, attr) {
                var watcher = scope.$watch(attr.ngShow, function ngShowWatchAction(visible){
                    console.log(scope); 
                    if(visible) {
                        scope.$eval(attr.onShow);
                        if(scope.fireOnce) {
                            console.log('watcher killed');
                            watcher(); // kill the watcher
                        }
                    }
                });
            }
        }
    }).
    directive('onShowFireOnce', function() {
        return {
            require: 'onShow',
            link: function(scope, element, attrs, onShowCtrl) {
                onShowCtrl.setFireOnce(true);
            }
        }
    });