GamepadButton

function gameLoop() {
  const gp = navigator.getGamepads()[0];
  if (gp.buttons[0].value > 0 || gp.buttons[0].pressed) {
    b--;
  } else if (gp.buttons[1].value > 0 || gp.buttons[1].pressed) {
    a++;
  } else if (gp.buttons[2].value > 0 || gp.buttons[2].pressed) {
    b++;
  } else if (gp.buttons[3].value > 0 || gp.buttons[3].pressed) {
    a--;
  }
  ball.style.left = `${a * 2}px`; // ball is a UI widget
  ball.style.top = `${b * 2}px`;
  requestAnimationFrame(gameLoop);
}