Holding a key would indeed require both on key down and up. I'd still argue that handling rerender on key down (or to fully match whatever OS/browser semantics, oninput) makes more sense than key up. Pressing Ctrl+V for example produces feedback as soon as "V" is pressed, not when Ctrl and/or V is released.

Interestingly Ctrl+V on OP's website does update immediately when Ctrl+V is pressed.