title: How to override event and still preform the old one?
body: <p>I'm looking for override event and still preform it's actions.</p>
  <p>Meaning something like this:</p>
  <pre><code>var oldOnError = window.onerror;
  window.onerror = function(msg, url, line) {
   oldOnError();
  };
  </code></pre>
  <p>Now this will get executed <strong>however</strong>, <code>onerror</code> event could accept several arguments and I don't and can't know which are there.</p>
  <p>So :</p>
  <ul>
  <li>Is there a simple solution for this?</li>
  <li>If not, how can i know what parameters <code>oldOnError</code> expecting to get?</li>
  </ul>