JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" name="pin1" class="pin" maxlength='4'>
<input type="text" name="pin2" class="pin" maxlength='4'>
<input type="text" name="pin3" class="pin" maxlength='4'>
<input type="text" name="pin4" class="pin" maxlength='4'>

JavaScript

$('.pin').keyup(function(){
    var pinLen = $(this).val().length;
    if(pinLen>=4){
         $(this).next().focus();          
    }                
});