title: Difference between defer().promise and Promise
body: <p>I know defer separates promises states control and process, here using Q as an example, the promise returned by <code>Q.defer().promise</code> and <code>Q.Promise</code> is totally different, why designing in this way? and what's the difference between these two "Promise"</p>
  
  <p>Thanks in advance</p>
  
  <p>PS: I'm currently working on a Promise library, issuses and PRS are welcomed: <a href="https://github.com/jiananshi/Promise-polyfill" rel="noreferrer">https://github.com/jiananshi/Promise-polyfill</a></p>