title: implement express controller class with typescript
body: <p>I'm doing an express app with typescript.
  The router code is:</p>
  
  <pre><code>let user = new User();
  router.get("/", user.test);
  </code></pre>
  
  <p>the user class is</p>
  
  <pre><code>export class User {
     test(req, res, next) {
        // this === undefined
     }
  }
  </code></pre>
  
  <p>the problem is that the this object is undefined inside test method. Is there a better way to implement express routing?</p>