if (obj !== obj) does somethig?
<p>In <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/indexOf#Compatibility" rel="nofollow">this page</a> you can see the following example of how to implement an indexOf for arrays:</p>

<pre><code>if (!Array.prototype.indexOf)
{
  Array.prototype.indexOf = function(searchElement /*, fromIndex */)
  {
    "use strict";

    if (this === void 0 || this === null)
      throw new TypeError();

    var t = Object(this);
    var len = t.length &gt;&gt;&gt; 0;
    if (len === 0)
      return -1;

    var n = 0;
    if (arguments.length &gt; 0)
    {
      n = Number(arguments[1]);
      if (n !== n)    // &lt;-- code of interest
        n = 0;
      else if (n !== 0 &amp;&amp; n !== (1 / 0) &amp;&amp; n !== -(1 / 0))
        n = (n &gt; 0 || -1) * Math.floor(Math.abs(n));
    }

    if (n &gt;= len)
      return -1;

    var k = n &gt;= 0
          ? n
          : Math.max(len - Math.abs(n), 0);

    for (; k &lt; len; k++)
    {
      if (k in t &amp;&amp; t[k] === searchElement)
        return k;
    }
    return -1;
  };
}
</code></pre>

<p>My question is about the line:</p>

<pre><code>if (n !== n)
</code></pre>

<p>in which case would this boolean expression return <code>true</code>?</p>
