title: How to do composite with gm node.js?
body: <p>How to do 'gm composite -gravity center change_image_url base_image_url' with GM Node.js?</p>
  
  <p>How to call <code>gm().command()</code> &amp; <code>gm().in()</code> or <code>gm().out()</code> to achieve the above?</p>