JSFiddle - React, Tailwind, and code Playground

HTML

<input class='validate' type='text'>

JavaScript

$(".validate").keyup(function(event){
         var val = $(this).val();
         if (val.length > 4){
            alert ("Max length is 4");
            val = val.substring(0, val.length - 1);
            $(this).val(val);
            $(this).focus();
            return false;
          }
   });