Userscript to give Gmail a Hey-like UX

tja.js

// ==UserScript==
// @name     Tja
// @version  1
// @grant    none
// ==/UserScript==

const elementType = {
  bottomBar: 'aeG',
  categoryList: 'nH oy8Mbf nn aeN',
  chromeDivs: 'nH nn',
  readEmail: 'zA yO',
  scrollBar: 'aeJ',
  searchBar: 'nH oy8Mbf qp',
  unreadEmail: 'zA zE'
};

function getElementByClass(className) {
  return document.getElementsByClassName(className)[0];
}

function getElementsByLiteralClassName(className) {
  return Array.prototype.filter.call(
    document.getElementsByClassName(className),
    el => el.className == className
  );
}

function manipulateElements(className, fn) {
  Array.prototype.forEach.call(
    document.getElementsByClassName(className),
    fn
  );
}

function hideElement(el) {
  el.style.display = 'none';
}

function showElement(el) {
  el.style.removeProperty('display');
}

function manipulator(type, fn) {
  return () => {
    manipulateElements(type, fn);
  };
}

function toggler(type) {
  return () => {
    const isHidden = getElementByClass(elementType[type]).style['display'] == 'none';
    manipulateElements(elementType[type], isHidden ? showElement : hideElement);
  };
}

function addScroll() {
  document.getElementById(':3').classList.add(elementType.scrollBar);
}

function removeScroll() {
  document.getElementById(':3').classList.remove(elementType.scrollBar);
}

function clutterise(fn) {
  ['bottomBar', 'categoryList', 'searchBar'].forEach(className =>
    fn(getElementByClass(elementType[className]))
  );
  getElementsByLiteralClassName(elementType.chromeDivs).forEach(fn);
}

function declutter() {
  clutterise(hideElement);
  removeScroll();
}

function reclutter() {
  clutterise(showElement);
  addScroll();
}

function isCluttered() {
  return document.getElementById(':3').classList.contains(elementType.scrollBar);
};

function toggleClutter() {
  if (isCluttered()) {
    declutter();
  } else {
    reclutter();
  }
}

function updateEventListeners(fn) {
  const listeners = {
    Comma: toggleClutter,
    Period: toggler('readEmail'),
    Slash: toggler('searchBar')
  };

  Object.keys(listeners).forEach(
    k => fn('keyup', event => {
      if (event.ctrlKey && event.code == k) {
        listeners[k]();
      }
    }));
}

function registerEventListeners() {
  updateEventListeners(document.addEventListener);
}

function unregisterEventListeners() {
  updateEventListeners(document.removeEventListener);
}

// Do the business!
registerEventListeners();