Input для подтвержения sms-кода

$('.number_input').on('keyup', function(e) { 
  let value = $(this).val(); 
  let len = value.length; 
  let curTabIndex = parseInt($(this).attr('tabindex')); 
  let nextTabIndex = curTabIndex + 1; 
  let prevTabIndex = curTabIndex - 1; 
  if (len >= 2) { 
    $(this).val(value.substr(0, 2)); 
    $('[tabindex=' + nextTabIndex + ']').focus(); 
  } else if (len == 0 && prevTabIndex !== 0) { 
    $('[tabindex=' + prevTabIndex + ']').focus(); 
  } 
});

input[type="number"] { 
  width: 40px; 
  height: 40px; 
  line-height: 40px; 
  border-radius: 5px; 
  font-size: 20px; 
} 
 
input[type=number]::-webkit-inner-spin-button, 
input[type=number]::-webkit-outer-spin-button { 
  -webkit-appearance: none; 
  -moz-appearance: none; 
  appearance: none; 
  margin: 0; 
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 
<input class="number_input" type="number" max_n=2 tabindex=1> 
<input class="number_input" type="number" max_n=2 tabindex=2> 
<input class="number_input" type="number" max_n=2 tabindex=3>