hypothetical/resources/assets/js/subscription.js

// subscription form functionality
function subscriptionFormInit() {
    var $form = $('#subscription-form'),
        $input = $form.find(':input'),
        $notify = $('#notification'),
        subscribe = {},
        submitting = false;

    var getSubscribeData = function() {
        subscribe = {
            name:    $('#name').val(),
            email:   $('#email').val(),
            address: $('#address').val(),
            _token:  $('#token').val()
        };
    };

    $('#submit').on('click', function(e) {
        e.preventDefault();
        var $submit = $(this);

        if (!submitting) {
            submitting = true;
            getSubscribeData();

            $.ajax({
                type: 'POST',
                url:  '/subscription-submit',
                data: subscribe
            }).always(function(response) {
                $form.find('.error').removeClass('error');
                $notify.removeClass('visible').removeClass('error');

                if (response === 'success') {
                    $form.addClass('success');

                    setTimeout(function() {
                        $notify.text('Thanks for subscribing!').addClass('success').addClass('visible');
                        $input.fadeOut(150);
                    }, 1000);
                } else {
                    var responseJSON = response.responseJSON,
                        errors = 0;

                    // add the error class to fields that haven't been filled out
                    for (var prop in responseJSON) {
                        if (responseJSON.hasOwnProperty(prop)) {
                            $('#' + prop).addClass('error');
                            errors++;
                        }
                    }

                    // if there are no errors with form fields then there must have been an API error
                    if (errors === 0)
                        $notify.text('An error occurred. Are you already subscribed?').addClass('error').addClass('visible');

                    // re-enable submitting
                    submitting = false;
                }
            });
        }
    });
}