index.js

$(document).ajaxError(function (e, xhr, settings, exception) {
    var STATUS_CODE_UNAUTHORIZED = 401,
        STATUS_CODE_FORBIDDEN = 403;

    // If we don't have a valid session, show a login form
    if (xhr.status === STATUS_CODE_UNAUTHORIZED || xhr.status === STATUS_CODE_FORBIDDEN) {
        showLoginForm();
    }
});