How can I test if an element is already visible?
<p>In the HTML code, I use jQuery to hide or display an element having an ID. How can I test if an element is already visible?</p>

<p>For example, we use <code>show()</code> to display an element having an ID. But before calling <code>show()</code>, I need to test  whether <code>show()</code> has been already used for that ID then how to compare?</p>
