fix(blog): fix TOCItems TypeError on direct page visit#646
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fumadocs-ui 16.9.1 changed TOCItems from a self-rendering component to a container that expects explicit TOCItem children. Without them, positions[] is always empty; when any heading enters the viewport the IntersectionObserver fires, TocThumb.calculate() accesses positions[activeIdx] which is undefined, and throws "Cannot read properties of undefined (reading '0')". The stale docs/pnpm-lock.yaml was pinning 16.6.5 locally while production (Vercel uses the root workspace lockfile) ran 16.9.1, hiding the breakage. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
rabisg
approved these changes
Jun 11, 2026
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Summary
TOCItemchildren toTOCItemsin the blog post page to fix aTypeError: Cannot read properties of undefined (reading '0')crash on direct visitdocs/pnpm-lock.yamlthat was pinningfumadocs-ui@16.6.5locally while production ran16.9.1Root cause
fumadocs-uiwas upgraded to16.9.1indocs/package.jsonbutdocs/pnpm-lock.yamlwasn't updated, causing a version split: Vercel (root workspace lockfile →16.9.1) vs local (stale docs lockfile →16.6.5).In
16.9.1,TOCItemschanged from a self-rendering component to a container that expectsTOCItemchildren. Without them:computed.positionsis always[](no anchor elements found in the DOM)IntersectionObserverfires while headings are already visible in the viewportTocThumb.calculate()runs withstartIdx >= 0, accessescomputed.positions[startIdx]→undefined→undefined[0]→ TypeErrorNavigation from
/blogdidn't throw because the observer fires asynchronously after the initial render, sostartIdx === -1andcalculate()returns early.Test plan
/blog/state-of-generative-ui-reportdirectly — no TypeError in console/blogto a post — no errors🤖 Generated with Claude Code