Try clicking on this box:

MouseEvent outcomes are:

altKey:
button (usually 0 = left, 1 = middle, 2 = right):
buttons (usually sum of 1 = left, 2 = right, 4 = middle, 8 = back, 16 = forward):
clientX:
clientY:
ctrlKey:
detail:
metaKey:
pageX:
pageY:
relatedTarget:
screenX:
screenY:
shiftKey:
which: