title: Mongoose error handling in one place
body: <p>I found in <a href="http://mongoosejs.com/docs/api.html#model_Model-save" rel="nofollow">mongoose docs</a> that I can handle errors generally, that I want. So you can do like:</p>
  
  <pre><code>Product.on('error', handleError);
  </code></pre>
  
  <p>But what is the signature of this <code>handleError</code> method? I want something like this:</p>
  
  <pre><code>handleError = (err) -&gt;
    if err
      console.log err
      throw err
  </code></pre>
  
  <p>But this doesn't work.</p>