title: Can anyone explain the use of $q service in angularjs?
body: <p>I am new to <code>angularjs</code>.I saw <code>$q</code> in restful api calls to check the promise.
  <code>$q.defer()</code> was used to retain the promise object.
  I read about the promises but I didn't get anything.
  although I can make the api call without <code>$q</code>, however it is used somewhere in articles.</p>
  
  <p>So I want to know the exact use of <code>$q</code> and difference in making api calls without <code>$q</code>.</p>
  
  <p>Kindly help.
  thanks   </p>