Detect Alt Gr (Alt Graph) modifier on key press

Question

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.

Answer 1

The altGraphKey in webkit browsers no longer appears to exist (as at September 2013) and the behaviour of Firefox has changed. Browser behaviours for the AltGr key currently appear to be:

• Webkit (Chrome) - ctrlKey: true, altKey: true
• IE 8 - ctrlKey: false, altKey: true
• IE 10 - ctrlKey: true, altKey: true
• Mozilla (Firefox) - ctrlKey: true, altKey: true

Which is to say, they are all currently consistent (apart from IE8, which remains consistently inconsistent).

The following snippet should catch Alt Gr - but not Alt or Ctrl - in modern browsers. You will need a special case for IE8 however:

if (event.ctrlKey && event.altKey) {
    // Appears to be Alt Gr
}

Answer 2

Disclaimer: I don't have a keyboard that has this key, so I can't test myself, but the spec says that can use the key property. This may be a good solution if you only need to support browsers that implement it (at time of writing, only Safari doesn't). You can check if the value is "AltGraph".

window.onkeydown = function (e) {
  if (e.key === 'AltGraph') {
    console.log(e.key);
  }
};

Answer 3

Worth mentioning is that it is possible to detect this in modern browser by checking the location of the alt key event.

See: Is there a way to detect which side the Alt key was pressed on (right or left)?