If u using controller & controllerAs in directive, then the link()'s 4th param 'controller' will refer to the controller u defined before.

 

function MessageController(){  var vm = this;    vm.message = "Hello"; }function greeting(){    function link(scope, element, attrs, ctrl){       ctrl.message = ctrl.message + ' ' + scope.name;    }      return {      controller: 'MessageController',      controllerAs: 'vm',      link: link,      scope: {        name: '@'      },      template: '
{
   {vm.message}}
'    };}angular.module('app', [])  .directive('greeting', greeting)  .controller('MessageController', MessageController);