bindToController, controllerAs, postLink w/ vm access

childDirective.js

function childDirective() {
  'ngInject';
  
  function postLink(scope, element, attribute, [vm, ParentController]) {
    // Initialization:
    
    ParentController.register(vm);
    
    // Handlers:
    
    element.on('click', (event) => {
      vm.triggerChild();
    });
  }
  
  return {
    bindToController: {
      child: '=',
      key: '@',
      onComplete: '&',
    },
    controller: 'ChildController',
    controllerAs: 'vm',
    link: postLink,
    require: ['ChildController', '^ParentController'],
    scope: {},
  };
}

export default childDirective;