Using onbeforeunload without dialog?

From the Mozilla Developer Network page:

When this event returns a non-void value, the user is prompted to
confirm the page unload.

This means the return value of the handler must be undefined (not '', false, or null) in order to avoid triggering the confirmation prompt.

window.onbeforeunload = function() {

  $.post("track.php", {
  ...
  });

  return undefined;
}

In javascript you can skip the return value altogether to get the same result.

In coffeescript with jquery it’s something like

$(document).ready ->
  $(window).bind('beforeunload', ->
    #put your cleanup code here
    undefined
  )