JSFiddle - React, Tailwind, and code Playground

HTML

<form method="POST">
    <input type="text" id="req1" required  />
    <input type="submit" />
</form>

CSS

body { padding: 20px; }
form { padding: 10px; }

JavaScript

var formulario = document.getElementsByTagName('form')[0],
    campo = document.getElementsByTagName('input')[0];

console.log(formulario);

formulario.noValidate = true;
formulario.addEventListener('submit', function(event) {
        if (!campo.disabled && !event.target.checkValidity()) {
            event.preventDefault();
            alert('No Valido');
        }else{
           alert('formulario enviado');
        }
    }, false);