Strange code in jQuery sources: var !== var ? x : y;
<p>Recently I found one weird line in the jQuery sources (last version 1.9.1, Sizzle package, line 129 <code>funescape</code> function):</p>

<pre><code>funescape = function( _, escaped ) {
    var high = "0x" + escaped - 0x10000;
    // NaN means non-codepoint
    return high !== high ?            // &lt;--- LINE 129
        escaped :
        // BMP codepoint
        high &lt; 0 ?
            String.fromCharCode( high + 0x10000 ) :
            // Supplemental Plane codepoint (surrogate pair)
            String.fromCharCode( high &gt;&gt; 10 | 0xD800, high &amp; 0x3FF | 0xDC00 );
};
</code></pre>

<p>What is the reason to make <code>high !== high</code> comparison? It obviously looks like <code>return escaped</code> will never be executed. Or do I miss something?</p>

<p><strong>Reference:</strong> <a href="https://github.com/jquery/sizzle/blob/master/sizzle.js#L129">https://github.com/jquery/sizzle/blob/master/sizzle.js#L129</a></p>
