https://www.generationrobots.com/blog/wp-content/themes/twentytwelve-child/js/navigation.js?ver=1.0

1/**
2 * navigation.js
3 *
4 * Handles toggling the navigation menu for small screens.
5 */
6( function() {
7	var nav = document.getElementById( 'site-navigation' ), button, menu;
8	if ( ! nav )
9		return;
10	button = nav.getElementsByTagName( 'h3' )[0];
11	menu   = nav.getElementsByTagName( 'ul' )[0];
12	if ( ! button )
13		return;
14
15	// Hide button if menu is missing or empty.
16	if ( ! menu || ! menu.childNodes.length ) {
17		button.style.display = 'none';
18		return;
19	}
20
21	button.onclick = function() {
22		if ( -1 == menu.className.indexOf( 'nav-menu' ) )
23			menu.className = 'nav-menu';
24
25		if ( -1 != button.className.indexOf( 'toggled-on' ) ) {
26			button.className = button.className.replace( ' toggled-on', '' );
27			menu.className = menu.className.replace( ' toggled-on', '' );
28		} else {
29			button.className += ' toggled-on';
30			menu.className += ' toggled-on';
31		}
32	};
33} )();
34
35document.addEventListener('DOMContentLoaded', function() {
36    var bodyClasses = document.getElementsByTagName('body')[0].className;
37    document.getElementById('responsiveMenuOpener').addEventListener('click', function(){
38        document.getElementsByTagName('body')[0].className = bodyClasses + ' responsiveMenuOpen';
39    });
40    document.getElementById('menuOverlay').addEventListener('click', function(){
41        document.getElementsByTagName('body')[0].className = bodyClasses;
42    });
43
44    document.getElementById('return-top').addEventListener('click', function(){
45        window.scrollToTop(200);
46    });
47
48    window.addEventListener('scroll', function(){
49        if (window.scrollY > 200){
50            document.getElementById('return-top').style.opacity = 1;
51        } else {
52            document.getElementById('return-top').style.opacity = 0;
53        }
54    });
55});
56
57function scrollToTop(scrollDuration) {
58    var scrollStep = -window.scrollY / (scrollDuration / 15),
59        scrollInterval = setInterval(function(){
60            if ( window.scrollY != 0 ) {
61                window.scrollBy( 0, scrollStep );
62            }
63            else clearInterval(scrollInterval);
64        },15);
65}
66
67/*
68document.addEventListener('DOMContentLoaded', function(){
69    var bodyClasses = document.getElementsByTagName('body')[0].className;
70    addClassResponsive(bodyClasses);
71
72    window.addEventListener('resize', function(){
73        addClassResponsive(bodyClasses);
74    });
75});
76
77function addClassResponsive(bodyClasses){
78    if(window.innerWidth <= 991){
79        if(window.innerWidth <= 767){
80            document.getElementsByTagName('body')[0].className = bodyClasses + ' mobile';
81        } else {
82            document.getElementsByTagName('body')[0].className = bodyClasses + ' tablet';
83        }
84    }
85}*/