1 files changed, 65 insertions, 0 deletions
diff --git a/docs/src/components/DocSidebar.tsx b/docs/src/components/DocSidebar.tsx
new file mode 100644
index 000000000..24e9dc4d9
--- /dev/null
+++ b/docs/src/components/DocSidebar.tsx
@@ -0,0 +1,65 @@
+import type { FunctionalComponent } from 'preact';
+import { h } from 'preact';
+import { useState, useEffect, useRef } from 'preact/hooks';
+import EditOnGithub from './EditOnGithub';
+
+const DocSidebar: FunctionalComponent<{ headers: any[]; editHref: string }> = ({
+  headers = [],
+  editHref,
+}) => {
+  const itemOffsets = useRef([]);
+  const [activeId, setActiveId] = useState<string>(undefined);
+
+  useEffect(() => {
+    const getItemOffsets = () => {
+      const titles = document.querySelectorAll('article :is(h1, h2, h3, h4)');
+      itemOffsets.current = Array.from(titles).map((title) => ({
+        id: title.id,
+        topOffset: title.getBoundingClientRect().top + window.scrollY,
+      }));
+    };
+
+    getItemOffsets();
+    window.addEventListener('resize', getItemOffsets);
+
+    return () => {
+      window.removeEventListener('resize', getItemOffsets);
+    };
+  }, []);
+
+  return (
+    <nav class="sidebar-nav">
+      <div class="sidebar-nav-inner">
+        <h2 class="heading">On this page</h2>
+        <ul>
+          <li
+            class={`header-link depth-2 ${
+              activeId === 'overview' ? 'active' : ''
+            }`.trim()}
+          >
+            <a href="#overview">Overview</a>
+          </li>
+          {headers
+            .filter(({ depth }) => depth > 1 && depth < 4)
+            .map((header) => (
+              <li
+                class={`header-link depth-${header.depth} ${
+                  activeId === header.slug ? 'active' : ''
+                }`.trim()}
+              >
+                <a href={`#${header.slug}`}>{header.text}</a>
+              </li>
+            ))}
+        </ul>
+        <h2 class="heading">More</h2>
+        <ul>
+          <li class={`header-link depth-2`}>
+            <EditOnGithub href={editHref} />
+          </li>
+        </ul>
+      </div>
+    </nav>
+  );
+};
+
+export default DocSidebar;