JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div id="obsah" class="sixteen columns clearfix">

    <form action="">
        <label><strong>Jméno:</strong><input type="text" value="" /><span></span></label>
    </form>

    </div>
</div>

JavaScript

$(document).ready(function(){
    $('input[type="text"]').blur(function(){
      if($(this).val().length < 3){
        $('span').text('Velmi malo');
      }
      else{
        $('span').text('Jo dobre');
      }
    });
});