Qiita_TOC_to_content.user.js

// ==UserScript==
// @name        Qiita_TOC_to_content
// @namespace   mino0123
// @include     http://qiita.com/*/items/*
// @include     http://qiita.com/*/private/*
// @version     1
// @grant       none
// ==/UserScript==

const subColumnEl = document.getElementsByClassName('col-sm-3')[0];

if (subColumnEl) {

  const observer = new MutationObserver((mutations) => {

    const tocTreeEl = document.getElementsByClassName('tocTree')[0];
    const contentEl = document.querySelector('.markdownContent.clearfix');// avoid slide
    const hasTocItem = tocTreeEl.getElementsByTagName('li').length > 0;

    if (tocTreeEl && contentEl && hasTocItem) {
      // Disconnect observer
      observer.disconnect();
      // Copy toc to content
      const cloneToc = tocTreeEl.cloneNode(true);
      cloneToc.className += ' tocToContent';
      contentEl.insertBefore(cloneToc, contentEl.firstChild);
      // Add styles
      const styleEl = document.createElement('style');
      styleEl.type = 'text/css';
      styleEl.innerHTML = `
                          .tocToContent {
                            width: 100% !important;
                            border: 1px solid #CCC;
                            font-size: 70%;
                          }
                          .tocToContent a {
                            display: inline !important;
                          }
                          `;
      document.head.appendChild(styleEl);
    }

  });

  observer.observe(subColumnEl, { childList: true, subtree: true });

}