show link to Github Pages source at gh-pages via tampermonkey

index.js

// ==UserScript==
// @name         Github Pages Source
// @version      1.4.0
// @description  Easily go to GitHub Pages' source repository
// @author       kidonng
// @namespace    https://github.com/kidonng/cherry
// @match        http*://*.github.io/*
// ==/UserScript==

;(() => {
  document.head.insertAdjacentHTML('beforeend', `<style>
    #page-source {
      position: fixed;
      right: 0;
      bottom: 0;
      margin: .5rem;
      opacity: .5;
      transition: opacity .25s;
    }
    #page-source:hover {
      opacity: 1;
    }
  </style>`)

  const username = location.host.slice(0, location.host.indexOf('github.io') - 1)
  let href = `https://github.com/${username}`
  let title
  if (document.title !== 'Site not found · GitHub Pages') {
    href += location.pathname.slice(0, location.pathname.indexOf('/', 1)) || `/${username}.github.io`
    title = 'Go to source repository'
  } else {
    title = 'Go to user profile'
  }

  // Icon is from GitHub header
  const icon = '<svg height="32" width="32" viewBox="0 0 16 16" version="1.1" aria-hidden="true"><path fill-rule="evenodd" d="M8 0C3.58 0 0 3.58 0 8c0 3.54 2.29 6.53 5.47 7.59.4.07.55-.17.55-.38 0-.19-.01-.82-.01-1.49-2.01.37-2.53-.49-2.69-.94-.09-.23-.48-.94-.82-1.13-.28-.15-.68-.52-.01-.53.63-.01 1.08.58 1.23.82.72 1.21 1.87.87 2.33.66.07-.52.28-.87.51-1.07-1.78-.2-3.64-.89-3.64-3.95 0-.87.31-1.59.82-2.15-.08-.2-.36-1.02.08-2.12 0 0 .67-.21 2.2.82.64-.18 1.32-.27 2-.27.68 0 1.36.09 2 .27 1.53-1.04 2.2-.82 2.2-.82.44 1.1.16 1.92.08 2.12.51.56.82 1.27.82 2.15 0 3.07-1.87 3.75-3.65 3.95.29.25.54.73.54 1.48 0 1.07-.01 1.93-.01 2.2 0 .21.15.46.55.38A8.013 8.013 0 0 0 16 8c0-4.42-3.58-8-8-8z"></path></svg>'

  document.body.insertAdjacentHTML('beforeend', `<a href="${href}" id="page-source" title="${title}">${icon}</a>`)
})()