No matter how quick you are, key events are received one at a time,
if you pressed 10 keys at once they would be processed in a queue.
When a keydown or keypress is handled you can look at
some boolean properties of the event:
ctrlKey,shiftKey,altKey each return true if the corresponding key was depressed
when the key event was handled.
Or you can build an array of key's on every keydown and wait to process them all when the next keyup event occurs.