title: delete a.x vs a.x = undefined
body: <p>Is there any substantial difference in doing either of these?</p>
  
  <pre><code>delete a.x;
  </code></pre>
  
  <p>vs</p>
  
  <pre><code>a.x = undefined;
  </code></pre>
  
  <p>where </p>
  
  <pre><code>a = {
      x: 'boo'
  };
  </code></pre>
  
  <p>could it be said that they are equivalent?</p>
  
  <p>(I'm not taking into account stuff like <a href="http://coding.smashingmagazine.com/2012/11/05/writing-fast-memory-efficient-javascript/" rel="noreferrer">"V8 likes not using <code>delete</code> better"</a>)</p>