title: why apache cordova keep Polling and XHR two ways to fetch data?
body: <p>when i read the source code of apache cordova. i find it has two ways to fecth the callback data from native code? </p>
  
  <p>why the author did'nt keep polling only?</p>
  
  <p>are there some issues exist?</p>
  
  <p>Thanks for your anwser!</p>