https://codeigniter.com/user_guide/_static/js/citheme.js?v=e0bcfc84

1/*
2 * Add classes to the body of each page of the documentation.
3 *
4 * From: [...]/outgoing/api_responses.html
5 * Into: ci-outgoing ci-api-responses
6 */
7window.onload = function() {
8	// Regular expression for finding chapter and subject in the current url
9	const regexUrl = new RegExp(/\/([a-z0-9_.-]+)\/([a-z0-9_.-]+)\.html/);
10
11	// Get the current url
12	const currentUrl = window.location.href;
13
14	// Get the document body
15	const documentBody = document.body;
16
17	// Placeholder for documentation index
18	var index = null;
19
20	if ((index = regexUrl.exec(currentUrl)) !== null)
21	{
22		// Sanitize the documentation chapter and subject
23		var chapter = sanitizeClass(index[1]);
24		var subject = sanitizeClass(index[2]);
25
26		// Documentation is generated into an html-folder for developers.
27		// This isn't a valid chapter. We are on documentation index.
28		if (chapter === 'html')
29		{
30			index = null;
31		}
32		// Add chapter and subject className(s) to the document body
33		else
34		{
35			addClass(documentBody, chapter);
36			addClass(documentBody, subject);
37		}
38	}
39
40	// No chapter and subject found. We are on documentation index.
41	if (index === null)
42	{
43		addClass(documentBody, 'documentation');
44		addClass(documentBody, 'index');
45	}
46}
47
48/**
49 * Sanitize the string - removing invalid characters
50 *
51 * @param {string} className className to be sanitized
52 *
53 * @return {string}
54 */
55sanitizeClass = function(className) {
56	return className.replace(/_/g, '-').replace(/[^a-z0-9-]/g, '');
57}
58
59/**
60 * Add class to HTML DOM Element Object
61 *
62 * @param {object} el         The HTML DOM Element Object
63 * @param {string} className  className to be added
64 * @param {string} namePrefix namePrefix to be added to className
65 *
66 * @return {void}
67 */
68addClass = function(el, className, namePrefix) {

69	namePrefix = namePrefix || 'ci-';
70
71	if (el.classList && className.length > 0)
72	{
73		el.classList.add(namePrefix + className);
74	}
75}