function OTPInput() {
  const inputs = document.querySelectorAll('#otp > *[id]');
  for (let i = 0; i < inputs.length; i++) {
    inputs[i].addEventListener('keydown', function(event) {
      if (event.key === "Backspace") {
        inputs[i].value = '';
        if (i !== 0)
          inputs[i - 1].focus();
      } else {
        if (i === inputs.length - 1 && inputs[i].value !== '') {
          return true;
        } else if (event.keyCode > 47 && event.keyCode < 58) {
          inputs[i].value = event.key;
          if (i !== inputs.length - 1)
            inputs[i + 1].focus();
          event.preventDefault();
        } else if (event.keyCode > 64 && event.keyCode < 91) {
          inputs[i].value = String.fromCharCode(event.keyCode);
          if (i !== inputs.length - 1)
            inputs[i + 1].focus();
          event.preventDefault();
        }
      }
    });
  }
}
OTPInput();