title: Access 'this' Inside Promise
body: <p>In the typescript function below, 'this' doesn't resolve to the instance of EmailValidator. How can I correct this function so it resolves to the correct instance of EmailVaildator and in turn, so that I can access _registerServices?</p>
  
  <pre><code>class EmailValidator {
  
      constructor(private _registerServices: RegisterServices) { }
  
      isAvailable(c: AbstractControl): Promise&lt;ValidationResult&gt; {
          let q = new Promise((resolve, reject) =&gt; {
              this._registerServices.emailIsAvailable(antiForgeryToken(), c.value)
                  .then(result =&gt; {
                      // Need to actually check the result.
                      resolve({ "emailtaken": true })
                  },
                  error =&gt; {
                      // Need to communicate the server error? Probably not.
                      resolve({ "servererror": true })
                  });
          });
  
          return q;
      }
  }
  </code></pre>