https://fitek.com.au/wp-content/themes/stable/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( 'menu-header_main_menu' ), 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	// Hide button if menu is missing or empty.
15	if ( ! menu || ! menu.childNodes.length ) {
16		button.style.display = 'none';
17		return;
18	}
19	button.onclick = function() {
20		if ( -1 == menu.className.indexOf( 'nav-menu' ) )
21			menu.className = 'nav-menu';
22		if ( -1 != button.className.indexOf( 'toggled-on' ) ) {
23			button.className = button.className.replace( ' toggled-on', '' );
24			menu.className = menu.className.replace( ' toggled-on', '' );
25		} else {
26			button.className += ' toggled-on';
27			menu.className += ' toggled-on';
28		}
29	};
30} )();