JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <input type="text"     name="ajax-username" />
    <input type="password" name="ajax-password" />
    <input type="submit" />
</form>

CSS

form { margin: 20px; }

JavaScript

document.querySelector( 'form' ).addEventListener( 'submit', function (e) {
    
    if (window.ajaxLogin) {
        ajaxLogin(function () {
            renderWelcomePage();
        });
    }
    
    this.innerHTML += '<br /> success';
    
    e.preventDefault();
    
}, false);