title: What is the consequence of this bit of javascript?
body: <p>I was looking at the jQuery UI code, and I found that every file starts with a construct like this:</p>
  
  <pre><code>jQuery.ui || (function($) {
  </code></pre>
  
  <p>My question is: why is there a semicolon before <code>jQuery</code>, and why is the logical OR being done?</p>