ng-if check if array is empty

To overcome the null / undefined issue, try using the ? operator to check existence:

<p ng-if="post?.capabilities?.items?.length > 0">

• Sidenote, if anyone got to this page looking for an Ionic Framework answer, ensure you use *ngIf:

  <p *ngIf="post?.capabilities?.items?.length > 0">
  

Verify the length property of the array to be greater than 0:

<p ng-if="post.capabilities.items.length > 0">
   <strong>Topics</strong>: 
   <span ng-repeat="topic in post.capabilities.items">
     {{topic.name}}
   </span>
</p>

Arrays (objects) in JavaScript are truthy values, so your initial verification <p ng-if="post.capabilities.items"> evaluates always to true, even if the array is empty.

post.capabilities.items will still be defined because it's an empty array, if you check post.capabilities.items.length it should work fine because 0 is falsy.