feat: show toc on mobile screens (#1964)

_javascript/modules/components/toc/toc-desktop.js

@@ -0,0 +1,22 @@
+export class TocDesktop {
+  /* Tocbot options Ref: https://github.com/tscanlin/tocbot#usage */
+  static options = {
+    tocSelector: '#toc',
+    contentSelector: '.content',
+    ignoreSelector: '[data-toc-skip]',
+    headingSelector: 'h2, h3, h4',
+    orderedList: false,
+    scrollSmooth: false,
+    headingsOffset: 16 * 2 // 2rem
+  };
+
+  static refresh() {
+    tocbot.refresh(this.options);
+  }
+
+  static init() {
+    if (document.getElementById('toc-wrapper')) {
+      tocbot.init(this.options);
+    }
+  }
+}

_javascript/modules/components/toc/toc-mobile.js

@@ -0,0 +1,117 @@
+/**
+ * TOC button, topbar and popup for mobile devices
+ */
+
+const $tocBar = document.getElementById('toc-bar');
+const $soloTrigger = document.getElementById('toc-solo-trigger');
+const $triggers = document.getElementsByClassName('toc-trigger');
+const $popup = document.getElementById('toc-popup');
+const $btnClose = document.getElementById('toc-popup-close');
+
+const SCROLL_LOCK = 'overflow-hidden';
+const CLOSING = 'closing';
+
+export class TocMobile {
+  static invisible = true;
+  static barHeight = 16 * 3; // 3rem
+
+  static options = {
+    tocSelector: '#toc-popup-content',
+    contentSelector: '.content',
+    ignoreSelector: '[data-toc-skip]',
+    headingSelector: 'h2, h3, h4',
+    orderedList: false,
+    scrollSmooth: false,
+    collapseDepth: 4,
+    headingsOffset: this.barHeight
+  };
+
+  static initBar() {
+    const observer = new IntersectionObserver(
+      (entries) => {
+        entries.forEach((entry) => {
+          $tocBar.classList.toggle('invisible', entry.isIntersecting);
+        });
+      },
+      { rootMargin: `-${this.barHeight}px 0px 0px 0px` }
+    );
+
+    observer.observe($soloTrigger);
+    this.invisible = false;
+  }
+
+  static listenAnchors() {
+    const $anchors = document.getElementsByClassName('toc-link');
+    [...$anchors].forEach((anchor) => {
+      anchor.onclick = this.hidePopup;
+    });
+  }
+
+  static refresh() {
+    if (this.invisible) {
+      this.initComponents();
+    }
+    tocbot.refresh(this.options);
+    this.listenAnchors();
+  }
+
+  static showPopup() {
+    TocMobile.lockScroll(true);
+    $popup.showModal();
+    const activeItem = $popup.querySelector('li.is-active-li');
+    activeItem.scrollIntoView({ block: 'center' });
+  }
+
+  static hidePopup() {
+    if (!$popup.open) {
+      return;
+    }
+
+    $popup.toggleAttribute(CLOSING);
+
+    $popup.addEventListener(
+      'animationend',
+      () => {
+        $popup.toggleAttribute(CLOSING);
+        $popup.close();
+      },
+      { once: true }
+    );
+
+    TocMobile.lockScroll(false);
+  }
+
+  static lockScroll(enable) {
+    document.documentElement.classList.toggle(SCROLL_LOCK, enable);
+    document.body.classList.toggle(SCROLL_LOCK, enable);
+  }
+
+  static clickBackdrop(event) {
+    const rect = event.target.getBoundingClientRect();
+    if (
+      event.clientX < rect.left ||
+      event.clientX > rect.right ||
+      event.clientY < rect.top ||
+      event.clientY > rect.bottom
+    ) {
+      TocMobile.hidePopup();
+    }
+  }
+
+  static initComponents() {
+    this.initBar();
+
+    [...$triggers].forEach((trigger) => {
+      trigger.onclick = this.showPopup;
+    });
+
+    $popup.onclick = this.clickBackdrop;
+    $btnClose.onclick = $popup.oncancel = this.hidePopup;
+  }
+
+  static init() {
+    tocbot.init(this.options);
+    this.listenAnchors();
+    this.initComponents();
+  }
+}