title: Is there anything wrong with using 'var undefined' to test for undefined
body: <p>Is there anything wrong with this test for undefined?</p>
  
  <pre><code>var undefined;
  
  if(x == undefined){
      //do something
  }
  </code></pre>
  
  <p>or this:</p>
  
  <pre><code>function undefined(x){
      return typeof x == 'undefined';
  }
  
  if(undefined(x)){
      //do something
  }
  </code></pre>
  
  <p>jsLint doesn't throws a reserverd word error, but the code still seems to work...</p>