Добавление класса к элементу по нажатию на кнопку

var loaded = function() {
  var App = {};
  App.dom = {
    links: document.querySelectorAll('a.module-link'),
    btnClose: document.querySelector('button.close'),
    loginForm: document.querySelector('.login_form'),
    headerTop: document.querySelector('.header-top'),
  };
 
  // [url]https://developer.mozilla.org/en-US/docs/Web/API/Document/cookie/Simple_document.cookie_framework[/url]  
  App.cookies = {
    set: function() {
      document.cookie = "showLoginForm=true; expires=Fri, 31 Dec 9999 23:59:59 GMT";
    },
    get: function() {
      return decodeURIComponent(document.cookie.replace(new RegExp("(?:(?:^|.*;)\\s*" + encodeURIComponent('showLoginForm').replace(/[\-\.\+\*]/g, "\\$&") + "\\s*\\=\\s*([^;]*).*$)|^.*$"), "$1")) || null;
    },
    remove: function() {
      document.cookie = "showLoginForm=; expires=Fri, 01 Jan 1970 00:00:00 GMT";
    }
  }
 
  App.showOrHideLoginForm = function() {
    var cl = this.dom.loginForm.classList,
      act = App.cookies.get() ? cl.add : cl.remove;
 
    act.call(this.dom.loginForm.classList, 'lf_visible');
    act.call(this.dom.headerTop.classList, 'ht_hidden');
  };
 
  App.click = function(block) {
    return function(event) {
      event.preventDefault();
      block();
      App.showOrHideLoginForm();
    };
  };
 
  App.linkClick = App.click(function() {
    App.cookies.set();
  });
 
  App.deleteClick = App.click(function() {
    App.cookies.remove();
  });
 
  for (var i = 0, l = App.dom.links.length; i < l; i++) {
    App.dom.links[i].addEventListener('click', App.linkClick);
  };
 
  App.dom.btnClose.addEventListener('click', App.deleteClick);
  App.showOrHideLoginForm();
};
 
window.addEventListener('DOMContentLoaded', loaded);

App.init = function() {
  // ...
  App.dom.btnClose.addEventListener('click', App.deleteClick);
  document.addEventListener('keydown', App.escClick);
  App.showOrHideLoginForm();
}
 
// ...
 
App.click = function(block) {
  return function(event) {
    block(event);
    App.showOrHideLoginForm();
  };
};
 
App.linkClick = App.click(function(e) {
  e.preventDefault();
  App.cookies.set();
});
 
App.deleteClick = App.click(function(e) {
  e.preventDefault();
  App.cookies.remove();
});
 
App.escClick = App.click(function(e) {
  if (e.keyCode !== 27) return;
  App.cookies.remove();
});