问AngularJS，我应该总是检查未定义的界限值吗？

EN

(function(){
  angular.module('myApp', [])
    .controller('MyCtrl', function($timeout){
      var ctrl = this;
      ctrl.model = {
        testA: 12,
        testB: undefined
      }
      
      $timeout(function(){
        ctrl.model.testB = "something here now"
      }, 5000)
      
    })
})();

pre{
background:yellow;
}

/*
Guarantees the elements aren't shown if they have ng-cloak
attribute, angular will remove this once it has processed the
directives on the element, at this point ng-if can take over
conditionally removing/adding the element or ng-hide can conditionally
remove it from display with css*/
[ng-cloak]{
  display:none;
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.6.6/angular.min.js"></script>


<div ng-app="myApp" ng-controller="MyCtrl as ctrl">
  <div>
    {{ctrl.model.testA}} <span ng-if="ctrl.model.testB" ng-cloak>-</span> {{ctrl.model.testB}}
  </div>
  
  <pre>{{ctrl|json}}</pre>
</div>