In Javascript, how do I tell if a user is pressing two keys at the same time?

Question

In Javascript, how do I tell if a user is pressing two keys at the same time?

For example, I have drawn a circle in the middle of the screen. I want to move it up while

Answer 1

Javascript keyboard events fire on keypress and keydown, but don't contain the additional keymask info to determine if other keys are pressed at the same time.