From https://geekalicious.pt/blog/en/javascript/submit-ajax-form-and-custom-validations-with-parsley-js

Parsley validate before ajax

$(document).ready(function() {
    $("form[name=myForm]").parsley();

    $("form[name=myForm]").on('submit', function(e) {
        var f = $(this);
        f.parsley().validate();

        if (f.parsley().isValid()) {
            alert('This form is valid');
            $.ajax({
                url: f.attr('action'),
                data: f.serialize(),
                type: 'post',
                dataType: 'json',
                success: function(response) {
                    alert('Congrats! Your form was successfully submitted.');
                },
                error: function() {
                    alert('Crap! There was something wrong.');
                }
            });
        } else {
            alert('This form isn't valid');
        }

        e.preventDefault();
    });
});