https://incode.com/js/behaviors/problem-tabs.js

1(function() {
2    if (window.__b_problemTabs) return;
3    window.__b_problemTabs = true;
4    function init() {
5        var wraps = [].slice.call(document.querySelectorAll("[data-problem-tabs]"));
6        wraps.forEach(function(wrap) {
7            var tabs = [].slice.call(wrap.querySelectorAll("[data-problem-tab]"));
8            var panes = [].slice.call(wrap.querySelectorAll("[data-problem-pane]"));
9            tabs.forEach(function(tab, i) {
10                tab.addEventListener("click", function() {
11                    tabs.forEach(function(t, k) {
12                        t.classList.toggle("is-active", k === i);
13                    });
14                    panes.forEach(function(p, k) {
15                        p.classList.toggle("is-active", k === i);
16                    });
17                });
18            });
19        });
20    }
21    if (document.readyState === "loading") {
22        document.addEventListener("DOMContentLoaded", init);
23    } else {
24        init();
25    }
26})();