User script to easily toggle document.designMode on a webpage

designModeToggler.user.js

// ==UserScript==
// @name     DesignMode toggler
// @version  1
// @grant    none
// @include	 *
// ==/UserScript==

const shortcut = {
  key: '1',
  ctrlKey: true,
  shiftKey: true,
}

const isShortcut = (sc, event) =>
  Object.keys(sc).reduce(
    (acc, propName) => sc[propName] === event[propName] && acc,
    true,
  )

document.addEventListener('keyup', e => {
  if (isShortcut(shortcut, e)) {
    document.designMode = document.designMode === 'off' ? 'on' : 'off'
  }
})