JSFiddle - React, Tailwind, and code Playground

HTML

<body ng-app="app" ng-controller="appCtrl">
  <test-directive activate="activate.initialValue"></test-directive>
</body>

JavaScript

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

app.controller('appCtrl', function($scope) {
  $scope.activate = {
    initialValue: 4
  }
});

app.directive('testDirective', function($timeout) {
  return {
    restrict: 'E',
    scope: {
      activate: '='
    },


    link: function(scope, elem, attrs) {
      scope.$watch('activate', function(newValue, oldValue) {
        console.log('activate has changed', newValue);
      });

      $timeout(function() {
        scope.activate = 0;
      }, 2000);
    },
    template: "{{activate}}"
  }
});