Difference in methods for testing undefined in javascript
<p>I've never understood the difference in these two ways for testing the existence of an object...</p>

<pre><code>typeof obj == "undefined"
</code></pre>

<p>vs.</p>

<pre><code>obj == undefined
</code></pre>

<p>Is one preferred? I'm almost always using jQuery, is the second a jQuery only feature?</p>
