Detect Alt Gr (Alt Graph) modifier on key press

In the javascript Event object, there are some boolean values to check if modifier keys are pressed:

• ctrlKey: CTRL key.
• altKey: ALT key.
• altLeft: ALT left key. Only for IE.
• altGraphKey: ALTGR key. Only for Chrome/Safari.

However, there are some issues:

• IE and Chrome set ctrlKey to true and altKey to true when you press the ALTGR modifier.
• Firefox sets ctrlKey to false and altKey to true when you press the ALTGR modifier, as only ALT has been pressed.
• Chrome has the altGraphKey property, but it is always undefined.

Question: how can I difference between an ALT+CTRL or an ALTGR key press? Specially in Chrome.