title: addEventListener not working with onbeforeunload
body: <pre><code>window.addEventListener("onbeforeunload",function() {return "are you sure?"});
  </code></pre>
  
  <p>^ This does not seem to work... at all... the page will simply close without displaying the confirmation box...</p>
  
  <p>I realize that...</p>
  
  <pre><code>window.onbeforeunload = function() {return "are you sure?"}
  </code></pre>
  
  <p>Will work, but I want to add to the functionality (e.g. add many event listeners to the "onbeforeunload" function) not rewrite the function completely!</p>