JSFiddle - React, Tailwind, and code Playground

HTML

<form id="target" action="javascript:alert( 'success!' );" method="post">
    Email: <input id='email' type='text'>
    <br><br>
    reEmail: <input id='reEmail' type='text'>
    <br><br>
    <input id='sub' type='submit'>
</form>

JavaScript

$(document).ready(function (){
    
    $('#reEmail').focusout(function () {
        email = $('#email').val();
        reEmail = $('#reEmail').val();
        if (email.length > 0)
        {
            if (reEmail == email)
            {
                $(this).css( "background-color", "#00ff00");
            }
            else
            {
                $(this).css( "background-color", "#ff0000");
            }
        }
        else
        {
            $(this).css( "background-color", "#fff");
        }
    });
    
    $('#target').submit(function () {
        email = $('#email').val();
        reEmail = $('#reEmail').val();
        
        if (email == reEmail && email.length > 0)
        {
            alert('OK');
            return;
        }
        
        alert('NO');
        event.preventDefault();
    });
});