title: ReferenceError: Can't find variable: dataKeys
body: <p>I'm working on an existing web application. I'm receiving some front-end errors that are fired for just one known user. The log says:</p>
  
  <blockquote>
    <p>[2014-05-19 18:40:05] frontend.ERROR: ReferenceError: Can't find variable: dataKeys {"file":"undefined","line":"13","browser":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.76.4 (KHTML, like Gecko) Version/7.0.4 Safari/537.76.4","page":"aPageFromTheSite"} []</p>
  </blockquote>
  
  <p>This error is fired from different pages on the site.</p>
  
  <p>I've tried to search the variable dataKeys:</p>
  
  <pre><code>grep -r "dataKeys" ./
  </code></pre>
  
  <p>but no results are found. I wonder where could it come from, since I'm not able to reproduce the error. I've also "googled", but no relevant results are found. Any idea of what it can be due to?</p>