JSFiddle - React, Tailwind, and code Playground

HTML

<form action="/echo/html/" id="myform" method="post">
    <input type="hidden" name="html" value="hi there" />
    <div id="log">ready.</div>
    <button>press me</button>
</form>

CSS

.ajax-loading {
    color: red;
}

JavaScript

$('myform').addEvent('submit', function (e) {
    e.stop();
    
    var log = $('log').empty().addClass('ajax-loading');
    
    new Request.HTML({
        data: this,
        update: log,
        onRequest: function(){
            log.addClass('ajax-loading');
        },
        onComplete: function(){
            log.removeClass('ajax-loading');
        }
    }).send();
});