Override JavaScript functionality

In case of that some JavaScript section needs to be modified, you can override the related method simply like following example:

DoubleOptinDownload.refreshFormFeedback = function (response) {
    jQuery('#download-message-success').slideUp();
    jQuery('#download-message-error').slideUp();
    for (let key in response.form) {
        let field = jQuery('#download-' + key + '-' + response.uid);
        let fieldWrapper = field.closest('.form-group');
        let fieldData = response.form[key];
        // Do what ever you like
        // ...
    }
};