Local Storage - Dark Theme Site Switcher

batman.js

// Set up the batman stylesheet link
const link = document.createElement('link');
link.href = '/css/batman.css';
link.rel = 'stylesheet';

const batmanHead = () => document.head.appendChild(link);
const batmanHeadRemove = () => document.head.removeChild(link);
const batmanLog = () => console.log(Array(16).join('hero'-1)+'Batman');

// If the theme is true, activate theme
if(localStorage.getItem('theme') === 'true') {
  batmanHead();
  batmanLog();
}

// Get the batman ID and if clicked,
document.getElementById('batman').addEventListener('click', function () {

  // if the theme is true, switch to false and remove the stylesheet link
  if(localStorage.getItem('theme') === 'true') {
    localStorage.setItem('theme', 'false');
    batmanHeadRemove();
  } else {
    localStorage.setItem('theme', 'true');
    batmanHead();
    batmanLog();
  }

});

// On pressing 'b', activate theme.
window.onkeydown = function(event) {
  if (event.keyCode == 66) {
    batmanHead();
    batmanLog();
    localStorage.setItem('theme', 'true');
  }
};

where is the html?