Level AWCAG 2.2
2.5.2 Pointer Cancellation
Functions operated by single pointer are not executed on the down-event.
Why it matters
Motor impairments
Tremors cause unintended clicks. If action fires on press, there's no way to undo.
Touch input
On touch screens, fingers are large and it's easy to mis-tap an adjacent button.
Cognitive disabilities
Users who operate slowly can cancel a mistake by releasing before the up-event.
All users
Everyone makes mistakes. Up-event activation makes 'never mind' possible.
Live demo
Pointer cancellation
It runs on mousedown, so accidental activation cannot be canceled.
↑ Activates as soon as you press down (mousedown)
Runs immediately on mousedown, so accidental activation cannot be undone
Understanding through personas
Nakamura (38) — Essential tremor
My hands tremble constantly, so my finger often slides off the intended button. UIs that act on mousedown are terrifying. With mouseup, I can release when I slip and cancel.