title: How can I add a property to a class dynamically in typescript?
body: <p>How can I add a property to a class in typescript?</p>
  
  <pre><code>export class UserInfo {
    public name:string;
    public age:number;
  }
  
  let u:UserInfo = new UserInfo();
  u.name = 'Jim';
  u.age = 10;
  u.address = 'London'; // Failed to compile. Property 'address' does not exist on type 'UserInfo'.
  </code></pre>
  
  <p>How to achieve this?</p>