title: No default engine was specified and no extension was provided
body: <p>I get the following error <code>No default engine was specified and no extension was provided</code> on trying to render template like the following:</p>
  
  <pre><code>app.get('/', function (req, res, next) {
      return res.render('index');
  });
  </code></pre>
  
  <p>In my server.js config I've added the following lines:</p>
  
  <pre><code>app.engine('jade', require('jade').__express);
  app.set('views', __dirname + '/views');
  </code></pre>
  
  <p>What's my problem?</p>
  
  <p><strong>EDIT:</strong> and what is <code>app.engine('jade', require('jade').__express);</code> mean and what cases should I use it?</p>