lifecycle:required

<lifecycle:required
       object="{string}">
</lifecycle:required>

<button class="tk-stl-button" ng-click="toggle()">Toggle</button>
<lifecycle:required object="value">
    <p>I only appear when "value" has a value.</p>
</lifecycle:required>

angular.module('lightning')
.controller('ExampleController', ['$scope', function($scope) {
                    $scope.toggle = function(){
                    if($scope.value == undefined){
                        $scope.value = 'A Value';
                    } else {
                        $scope.value = undefined;
                    }
                    }
                }]);