title: NodeJS - wait for callbacks to finish
body: <p>Pusedo-code:</p>
  
  <pre><code>app.get('/', (req, res) =&gt; {
      request(url, callback1) //callback1 alters 'index' template a bit
      request(url, callback2) //callback2 alters 'index' template a bit
      request(url, callback3) //callback3 alters 'index' template a bit
  
      res.render('index'); //Have to render after callback1,2,3 are done
  });
  </code></pre>
  
  <p>How do I make sure <code>render</code> is only called after all callbacks are resolved?</p>
  
  <p>PS. The URLs are different for each call.</p>