title: What is the purpose of passing-in undefined?
body: <p>I have noticed <code>jQuery</code> and related keynote plugins like <code>jQuery.UI</code> pass <code>undefined</code> as a parameter into anonymous functions used in their module definitions, like so:</p>
  
  <pre><code>(function($, undefined) { ... })(jQuery);
  </code></pre>
  
  <p>Alternatively, I have noticed other plugins recommended by jQuery and/or others do NOT pass undefined in as a parameter.</p>
  
  <p>This is probably a silly question, but...</p>
  
  <p>Shouldn't it always be available anyway?  Why pass it in?  Is there some sort of other purpose or trick going on here?</p>