JSFiddle - React, Tailwind, and code Playground

HTML

<body ng-app="main">
    <box></box>
</body>

JavaScript

angular.module('main', [])
.directive('box', function() {
    return {
        restrict: 'E',
        controller: function() { },
        require: '?^box',
        link: function(scope, iElement, iAttrs, controller) {
            alert('Controller found: ' + (controller !== undefined));
        }
    };
});