title: How do you access values passed to next() functions in Node
body: <p>I'm using <em>Node</em> with <em>Express.js</em> to write a back-end for a project I'm working on.</p>
  
  <p><code>next()</code> functions are used in middleware to move to the next piece in the middleware chain, and finally onto the <code>app.VERB()</code> function. Where and how (further down the line) do I access this variable?</p>
  
  <p>Example code:</p>
  
  <pre><code>app.use(function (req, res, next) {
  
      User.findOne({
              'email': emailValue
          }, function (err, foundUser) {
  
              if (err) return next(err); 
  
              // Else do something
          }
      }); 
  });
  </code></pre>
  
  <p>What has access to the <code>err</code> value passed to <code>next()</code>?</p>