In JavaScript, where does "constructor" come from?
<p>The following snippet of code is taken from Eloquent JavaScript.</p>

<pre><code>var noCatsAtAll = {};
if ("constructor" in noCatsAtAll)
  console.log("Yes, there definitely is a cat called 'constructor'.");
</code></pre>

<p>I find it quite mystifying. Why does the 'if' return true?</p>
