feat: make the table of contents sections reactive to user-scroll

Author: SeanCassiere

app/components/Doc.tsx

@@ -43,6 +43,55 @@ export function Doc({
 
   const isTocVisible = shouldRenderToc && headings && headings.length > 1
 
+  const markdownContainerRef = React.useRef<HTMLDivElement>(null)
+  const [activeHeadings, setActiveHeadings] = React.useState<Array<string>>([])
+
+  const headingElementRefs = React.useRef<
+    Record<string, IntersectionObserverEntry>
+  >({})
+
+  React.useEffect(() => {
+    const callback = (headingsList: Array<IntersectionObserverEntry>) => {
+      headingElementRefs.current = headingsList.reduce(
+        (map, headingElement) => {
+          map[headingElement.target.id] = headingElement
+          return map
+        },
+        headingElementRefs.current
+      )
+
+      const visibleHeadings: Array<IntersectionObserverEntry> = []
+      Object.keys(headingElementRefs.current).forEach((key) => {
+        const headingElement = headingElementRefs.current[key]
+        if (headingElement.isIntersecting) {
+          visibleHeadings.push(headingElement)
+        }
+      })
+
+      if (visibleHeadings.length >= 1) {
+        setActiveHeadings(visibleHeadings.map((h) => h.target.id))
+      }
+    }
+
+    const observer = new IntersectionObserver(callback, {
+      rootMargin: '0px',
+      threshold: 0.2,
+    })
+
+    const headingElements = Array.from(
+      markdownContainerRef.current?.querySelectorAll(
+        'h2[id], h3[id], h4[id], h5[id], h6[id]'
+      ) ?? []
+    )
+    headingElements.forEach((el) => observer.observe(el))
+    console.log(
+      'observing',
+      headingElements.map((h) => h.id)
+    )
+
+    return () => observer.disconnect()
+  }, [])
+
   return (
     <div
       className={twMerge(
@@ -61,9 +110,11 @@ export function Doc({
         <div className="h-px bg-gray-500 opacity-20" />
         <div className="h-4" />
         <div
+          ref={markdownContainerRef}
           className={twMerge(
             'prose prose-gray prose-sm prose-p:leading-7 dark:prose-invert max-w-none',
-            isTocVisible && 'pr-4 lg:pr-6'
+            isTocVisible && 'pr-4 lg:pr-6',
+            'styled-markdown-content'
           )}
         >
           <Markdown htmlMarkup={markup} />
@@ -83,7 +134,12 @@ export function Doc({
 
       {isTocVisible && (
         <div className="border-l border-gray-500/20 max-w-52 w-full hidden 2xl:block transition-all">
-          <Toc headings={headings} colorFrom={colorFrom} colorTo={colorTo} />
+          <Toc
+            headings={headings}
+            activeHeadings={activeHeadings}
+            colorFrom={colorFrom}
+            colorTo={colorTo}
+          />
         </div>
       )}
     </div>

app/components/Toc.tsx

@@ -1,7 +1,6 @@
 import * as React from 'react'
 import { twMerge } from 'tailwind-merge'
 import { HeadingData } from 'marked-gfm-heading-id'
-import { useLocation } from '@tanstack/react-router'
 
 const headingLevels: Record<number, string> = {
   1: 'pl-2',
@@ -16,17 +15,15 @@ type TocProps = {
   headings: HeadingData[]
   colorFrom?: string
   colorTo?: string
+  activeHeadings: Array<string>
 }
 
-export function Toc({ headings, colorFrom, colorTo }: TocProps) {
-  const location = useLocation()
-
-  const [hash, setHash] = React.useState('')
-
-  React.useEffect(() => {
-    setHash(location.hash)
-  }, [location])
-
+export function Toc({
+  headings,
+  colorFrom,
+  colorTo,
+  activeHeadings,
+}: TocProps) {
   return (
     <nav className="flex flex-col sticky top-2 max-h-screen divide-y divide-gray-500/20">
       <div className="p-2">
@@ -48,7 +45,7 @@ export function Toc({ headings, colorFrom, colorTo }: TocProps) {
             <a
               title={heading.id}
               href={`#${heading.id}`}
-              aria-current={hash === heading.id && 'location'}
+              aria-current={activeHeadings.includes(heading.id) && 'location'}
               className={`truncate block aria-current:bg-gradient-to-r ${colorFrom} ${colorTo} aria-current:bg-clip-text aria-current:text-transparent`}
               dangerouslySetInnerHTML={{
                 __html: heading.text,

app/routes/$libraryId/$version.docs.framework.$framework.$.tsx

@@ -48,6 +48,7 @@ function Docs() {
   return (
     <DocContainer>
       <Doc
+        key={filePath}
         title={title}
         content={content}
         repo={library.repo}