Toggle left sidebar button for jsfiddle.net

jsfiddle.js

const prefix = 'VdMj';
const class_hidden = `${prefix}-hidden-sidebar`;
const class_button = `${prefix}-menu-button`;

const styles = [
  `body.${class_hidden} #sidebar { display: none !important }`,
  `body.${class_hidden} #content { margin-left: 0 !important }`,
  `#actions > nav > div:first-child > a.${class_button} {
    font-size: 1.6em;
    font-family: segoe ui symbol, apple color emoji, segoe ui emoji, notocoloremoji, android emoji, emojisymbols, emojione mozilla;
  }`
];

const newMenuButton = (text, title, href, onclick) => {
  const div = doc.createElement('div');
  const a = doc.createElement('a');
  div.appendChild(a);
  div.classList.add('actionItem');
  a.classList.add('aiButton', '${class_button}');
  a.textContent = text;
  a.onclick = onclick;
  a.title = title;
  a.href = href;
  if (href) a.target = '_blank';
  return div;
}

const doc = document,
      body = doc.body,
      style = doc.createElement('style');

//
// Add buttons: ☰, ⇪ Preview
//

const storage = localStorage;
const update = (el, cl, flag) => {
  el.textContent = flag ? '⋮' : '☰';
  flag ? cl.add(class_hidden) : cl.remove(class_hidden);
}

const buttonToggleSidebar = newMenuButton('☰', 'Hide left sidebar menu', '', function () {
  update(this, body.classList, storage[class_hidden] ^= 1);
  return false;
});

// https://jsfiddle.net/css/dist-editor-dark.css
const theme = doc.querySelector('link#editor-theme[rel="stylesheet"][href*="dark.css"]') ? 'dark/' : '';

const buttonPreviewMode = newMenuButton('⇪ Preview', 'Switch to preview mode',
  doc.location.href.replace(/\/*(?:#.*?)?$/, '/embedded/result,html,css,js/') + theme);

const target = doc.querySelector('#actions > nav');

target.insertBefore(buttonToggleSidebar, target.firstChild);

if (doc.getElementById('editor')) {
  target.appendChild(buttonPreviewMode);
}

update(buttonToggleSidebar.firstChild, body.classList, storage[class_hidden] *= 1);

doc.head.appendChild(style);
styles.forEach((rule, index) =>
  style.sheet.insertRule(rule, index));

jsfiddle.svg

manifest.json

{
  "manifest_version": 2,
  "name": "Toggle sidebar button for jsfiddle.net",
  "description": "Toggle left sidebar button for jsfiddle.net",
  "version": "0.0.0.1",
  "icons": {
     "32": "ico/jsfiddle-32x32.png",
     "48": "ico/jsfiddle-48x48.png",
    "128": "ico/jsfiddle-128x128.png",
    "256": "ico/jsfiddle-256x256.png"
  },
  "content_scripts": [{
    "js": ["jsfiddle.js"],
    "matches": ["*://jsfiddle.net/*"],
    "run_at": "document_end"
  }],
  "permissions": ["*://jsfiddle.net/*"]
}