Why are cross-frame or -window arrays in Javascript so hard to identify?
<p>Crockford poses a solution in <em>Javascript: The Good Parts</em> for identifying if an object is an array which goes something like this:</p>

<pre><code>var isArray = function (obj) {
   return obj &amp;&amp; typeof obj === "object" &amp;&amp; obj.constructor === Array;
}
</code></pre>

<p>But then he goes on to state that </p>

<blockquote>
  <p>...it fails to identify arrays that were constructed in a different window or frame...</p>
</blockquote>

<p>Why doesn't this solution work in that situation?</p>
