</span>(<span class="string">'wahoo'</span>)).<span class="variable">listen</span>(<span class="number integer">3000</span>);
</code></pre>

<p>To pass control to the next middleware layer, we may call the <code>next()</code> function with an optional instanceof <code>Error</code>.
Middleware with four parameters is an error handling middleware, the <code>err</code> object can then be logged, used to issue a response, ignored, etc.</p>

<pre><code class="js"><span class="keyword">function</span> <span class