title: JavaScript class definition without instanciation
body: <p>I'd like to define an empty data class in JS to fill it with JSON afterwards.
  In c# I'd do something like that :</p>
  
  <pre><code>class Person {
      string name;
      int age;
      Person[] children;
      var whatever;
  }
  </code></pre>
  
  <p>This doesn't work, the IDE doesn't like it : "Unexpected token. A constructor, method, accessor, or property was expected". </p>
  
  <p>I've tried </p>
  
  <pre><code>class Person {
      var name;
      var age;
      var children;
      var whatever;
  }
  </code></pre>
  
  <p>but I have no experience with JS, and everywhere I see that declared variables are defined right away. </p>
  
  <p>I don't understand the error since I believe those are properties, and I don't know the behaviour of the JSON deserializer regarding arrays of objects, knowing said objects might be missing properties in the JSON but I'd still want them to be declared (but not set) in the JS object created from the string.</p>
  
  <p>How can I make things work ?</p>