Keyboard Alt Modifier Cannot Be Overridden

I'm writing a Javascript class to handle keystrokes as well as keystroke combinations. For example, the following would add a callback for the SHIFT key. MYAPP.Keyboard.instance()

Solution 1:

This may help as an example. At the bottom of the page the author claims that his script overrides all modifiers - Ctrl, Alt, Shift, Meta. Hope this help, somehow.