JSFiddle - React, Tailwind, and code Playground
HTML
<input type="text" name="pin1" id="pin1">
<br>
<input type="text" name="pin2" id="pin2">
JavaScript
$('#pin1').keyup(function(){
var pin1Len = $('#pin1').val().length;
if(pin1Len==4){
$('#pin2').focus();
}
});