https://futsutsuka.net/en/assets/js/lang.js

1/**
2 * Persist language choice from JP/EN toggle (sessionStorage).
3 */
4(function () {
5	var STORAGE_KEY = 'futsutsuka_lang';
6
7	function resolveLang(link) {
8		var lang = link.getAttribute('data-futsutsuka-lang');
9		if (lang === 'ja' || lang === 'en') {
10			return lang;
11		}
12		var label = (link.textContent || '').replace(/\s+/g, '').trim().toUpperCase();
13		if (label === 'EN') {
14			return 'en';
15		}
16		if (label === 'JP' || label === 'JA') {
17			return 'ja';
18		}
19		var href = link.getAttribute('href') || '';
20		if (/\/en\/?$|\/en\/|\/en\.html/i.test(href)) {
21			return 'en';
22		}
23		return 'ja';
24	}
25
26	document.addEventListener('click', function (e) {
27		var link = e.target.closest('.header__langLink');
28		if (!link) {
29			return;
30		}
31		var lang = resolveLang(link);
32		try {
33			sessionStorage.setItem(STORAGE_KEY, lang);
34		} catch (err) {}
35	}, true);
36})();