userscript to beautify js and css files

jsbeautify.js

// ==UserScript==
// @name         jsbeautify
// @namespace    https://gist.github.com/martianyi/ba41ece11e2815bce17fff02793a8197/
// @version      0.1
// @description  beautify js and css files
// @author       martianyi
// @match        *://*/*
// @require      https://cdnjs.cloudflare.com/ajax/libs/js-beautify/1.7.5/beautify.min.js
// @require      https://cdnjs.cloudflare.com/ajax/libs/js-beautify/1.7.5/beautify-css.min.js
// @require      https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/highlight.min.js
// @resource     hlCSS https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/github.min.css
// @grant    GM_addStyle
// @grant    GM_getResourceText
// ==/UserScript==

(function() {
    'use strict';
    var hlCSS = GM_getResourceText ("hlCSS");
    GM_addStyle (hlCSS);
    var isJS = location.href.match(/\.js(?:\?|$)/);
    var isCSS = location.href.match(/\.css(?:\?|$)/);
    var preEl = document.querySelector('pre');
    var btn;
    if (preEl && (isJS || isCSS)) {
        btn = document.createElement('button');
        btn.textContent = 'beautify';
        btn.addEventListener('click', beautify);
        document.body.insertBefore(btn, preEl);
    }
    function beautify() {
        var code = preEl.textContent;
        if (isJS) code = js_beautify(code);
        else if (isCSS) code = css_beautify(code);
        document.body.removeChild(btn);
        var codeEl = document.createElement('code');
        codeEl.textContent = code;
        preEl.textContent = '';
        preEl.appendChild(codeEl);
        hljs.initHighlighting();
    }
})();