title: How to add a Worksheet function in Google Apps Script?
body: <p>I want to use a built-in function in a Google Apps script. 
  Something similar to VBA <code>WorksheetFunction</code>
  How can I achieve that?</p>
  
  <p>For example, how to include in the script:</p>
  
  <pre><code>var foo=DATEVALUE(mydate);
  </code></pre>