JSFiddle - React, Tailwind, and code Playground

HTML

<form action="domain_management.php" method="get">
    <input type="text" name="whitelist_add" id="whitelist_add" placeholder="domain.com">
    <button type="submit" class="btn btn-success whitelistCheck" disabled='disabled'>Add to Whitelist</button>
</form>

JavaScript

$(function () {
    $('#whitelist_add').keyup(function () {
        if ($(this).val() == '') { //Check to see if there is any text entered
            //If there is no text within the input, disable the button
            $('.whitelistCheck').attr('disabled', 'disabled');
        } else {
            // Domain name regular expression
            var regex = new RegExp("^([0-9A-Za-z-\\.@:%_\+~#=]+)+((\\.[a-zA-Z]{2,3})+)(/(.)*)?(\\?(.)*)?");
            if (regex.test($(this).val())) {
                // Domain looks OK
                //alert("Successful match");
                $('.whitelistCheck').removeAttr('disabled');
            } else {
                // Domain is NOT OK
                //alert("No match");
                $('.whitelistCheck').attr('disabled', 'disabled');
            }
        }
    });
});