There is the standard event.getModifierState() API, but the most reliable solution I found was to listen for "keydown", "keyup", "blur", "pointerdown", "pointermove" and "pointerup" events on the window object and then store the modifier keys state based on the value of event.ctrlKey/altKey/metaKey/shiftKey.

You need to listen for the pointer events because some devices such as Wacom tablets do not dispatch proper keyboard events when you press a button that has a modifier key role assigned to it.

On Apple devices event.metaKey represents the state of the command key, so in most scenarios you would be storing the state as: let ctrlOrCmd = (isAppleDevice ? event.metaKey : event.ctrlKey);