title: Javascript Promise object with GWT JsInterop
body: <p>I have this code that I want to use to init() a third-party Javascript library:</p>
  
  <pre><code>@JsType(namespace = JsPackage.GLOBAL, name = "Kinvey", isNative = true)
  public class Kinvey {
      public String appKey;
      public String appSecret;
      public static native void init();
  }
  </code></pre>
  
  <p>The problem is the <code>init</code> function returns a Javascript Promise object, <strong>how can GWT deal with this object using JsInterop?</strong></p>
  
  <pre><code>var promise = Kinvey.init({
      appKey    : 'your_app_key',
      appSecret : 'your_app_secret'
  });
  promise.then(function(activeUser) {
      ...
  }, function(error) {
      ...
  });
  </code></pre>