what does frame mean in javascript?
<p>I am reading the book "maintainable javascript".   in the book, the author talks about the frame, need help to understand what that means.</p>

<blockquote>
  <p>Passing arrays back and forth <strong>between frames</strong> was one of the original <strong>cross-frame issues</strong>
  in JavaScript. Developers quickly discovered that instanceof Array didn’t always produce
  appropriate results in these cases. As mentioned previously, <strong>each frame</strong> has its
  own Array constructor, so an instance from one <strong>frame</strong> isn’t recognized in another.
  Douglas Crockford first recommended performing some duck typing, testing for the
  presence of the sort() method:</p>
</blockquote>

<pre><code>// Duck typing arrays
function isArray(value) {
  return typeof value.sort === "function";
}
</code></pre>
