1 files changed, 61 insertions, 0 deletions
diff --git a/examples/docs/src/components/DocSidebar.tsx b/examples/docs/src/components/DocSidebar.tsx
new file mode 100644
index 000000000..076d460cc
--- /dev/null
+++ b/examples/docs/src/components/DocSidebar.tsx
@@ -0,0 +1,61 @@
+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(h2, h3, h4)');
+      itemOffsets.current = Array.from(titles).map((title) => ({
+        id: title.id,
+        topOffset: title.getBoundingClientRect().top + window.scrollY,
+      }));
+    };
+
+    const onScroll = () => {
+      const itemIndex = itemOffsets.current.findIndex((item) => item.topOffset > window.scrollY + window.innerHeight / 3);
+      if (itemIndex === 0) {
+        setActiveId(undefined);
+      } else if (itemIndex === -1) {
+        setActiveId(itemOffsets.current[itemOffsets.current.length - 1].id);
+      } else {
+        setActiveId(itemOffsets.current[itemIndex - 1].id);
+      }
+    };
+
+    getItemOffsets();
+    window.addEventListener('resize', getItemOffsets);
+    window.addEventListener('scroll', onScroll);
+
+    return () => {
+      window.removeEventListener('resize', getItemOffsets);
+      window.removeEventListener('scroll', onScroll);
+    };
+  }, []);
+
+  return (
+    <nav>
+      <div>
+        <h4>Contents</h4>
+        <ul>
+          {headers
+            .filter(({ depth }) => depth > 1 && depth < 5)
+            .map((header) => (
+              <li class={`header-link depth-${header.depth} ${activeId === header.slug ? 'active' : ''}`.trim()}>
+                <a href={`#${header.slug}`}>{header.text}</a>
+              </li>
+            ))}
+        </ul>
+      </div>
+      <div>
+        <EditOnGithub href={editHref} />
+      </div>
+    </nav>
+  );
+};
+
+export default DocSidebar;