JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.3.20/angular.js"></script>
<parent-directive>
    <button ng-click="parentCtrl.toggle()">Toggle message</button>
    <child-directive>
        <p>{{childCtrl.someProperty}}</p>
    </child-directive>
</parent-directive>

JavaScript

var myApp = angular.module('myApp', []);

myApp.directive('parentDirective', function ($timeout) {
    return {
        restrict: 'E',
        scope: true,
        controllerAs: 'parentCtrl',
        controller: function () {
            var vm = this;
            vm.someProperty = true;
            vm.toggle = function () {
                vm.someProperty = !vm.someProperty;
            }
        },
        link: function (scope, element, attrs, controller) {
            $timeout(function () {
                console.log('timeout fired');
                controller.toggle();
            }, 1000);
        }
    }
});

myApp.directive('childDirective', function () {
    return {
        restrict: 'E',
        scope: true,
        require: ['childDirective', '^parentDirective'],
        controllerAs: 'childCtrl',
        controller: function () {
            var vm = this;
            vm.someProperty = '';
        },
        link: function (scope, element, attrs, controllers) {

            var controller = controllers[0];
            var parentController = controllers[1];

            scope.$watch('parentController.someProperty', function () {
                controller.someProperty = parentController.someProperty 
                    ? 'Hello world!' : 'Goodbye cruel world';
            });
        }
    }
});