title: durandal.js confirmation box not able to return yes or no
body: <p>i would like to add comfirmationbox in durandal.js</p>
  
  <p>i wrote following to code , but it is not returning Yes or NO</p>
  
  <pre><code>define(['services/logger', 'durandal/plugins/router', 'durandal/app'], function (logger, router, app) {
  
  if (app.showMessage('Are you sure you want to delete :' + titlename + '?', 'Delete Confirmation', ['Yes', 'No'])) {
                  DeleteAchievement(self, obj.Soid)
              }
  </code></pre>