title: Best practice to extend objects in underscore.js
body: <p>I know that extending objects is done via the </p>
  
  <pre><code>_.extend(parent, child);
  </code></pre>
  
  <p>method.</p>
  
  <p>I've seen different places in the web where people are extending objects in a special way in underscore.js</p>
  
  <pre><code>_.extend({}, this, child);
  </code></pre>
  
  <p>Why do they do that?</p>