title: Javascript Variable Declaration with ||
body: <p>I'm investigating Three.js at the moment and have come across this variable declaration at the top of the main source file:</p>
  
  <pre><code>var THREE = THREE || { REVISION: '52' };
  </code></pre>
  
  <p>I'm just wondering what the OR (||) is doing in there - what is the function of it?</p>