title: Equivalent of c# class virtual member in TypeScript
body: <p>So in C# when I've been creating model classes and lazy loading things, I do something like this:</p>
  
  <pre><code>public int? User_ID { get; set; }
  public int? Dept_ID { get; set; }
  </code></pre>
  
  <p>Then a little farther down in my class I pop in my virtuals like so:</p>
  
  <pre><code>public virtual User User {get; set;}
  public virtual Department Dept {get; set;}
  </code></pre>
  
  <p>How would I do this in Typescript? Something like this?:</p>
  
  <pre><code>User_ID: number;
  Dept_ID: number;
  User: User;
  Dept: Department;
  </code></pre>
  
  <p>I don't think interfaces is what I want/need...but then again protected doesn't seem correct either.  Something tells me I'm missing an obvious answer here.</p>