JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://parsleyjs.org/parsley.js"></script>
<form id="myform">
    <input type="text" data-parsley-myvalidator="foo" data-parsley-required />
    <input type="submit" />
</form>

JavaScript

$('#myform').parsley({
    validators: {
        myvalidator: function () {
            return {
                validate: function (value, requirements) {
                    alert('myvalidator');
                    return false;
                },
                priority: 32
            }
        }
    },
    messages: {
        myvalidator: 'my validator failed'
    }
});