Value changed when using $.extend()
<p>I am using <code>$.extend()</code> to make a copy of a data set. Most time it works OK. But for some certain data set. The copy would be different from the original one.</p>

<p>For example, the following is the code.</p>

<pre><code>console.log(dataset[key].data)
var dataTemps = $.extend(true, [], dataset[key]);         
console.log(dataTemps.data);
</code></pre>

<p>For the first console.log, the log was something like</p>

<pre><code>Array[7]=[1,1, null, "academicreport",330, 22, "M.Sc"]
</code></pre>

<p>But for the second console.log, the log was </p>

<pre><code>Array[7]=[1,1, null, NaN,330, 22, "M.Sc"]
</code></pre>

<p>Does anyone know how the <code>$.extend</code> changed the value of <code>data[3]</code> from <code>"academicreport"</code> to <code>NaN</code>?</p>
