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fix(md): let layouts read the page frontmatter with React, Solid and Svelte - #475
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`useFrontmatter()` in a layout that wraps a `.md` page returned `{}`
with React, Solid and Svelte. The frontmatter was provided only inside
the page component, below its layouts.
The island renderer now provides the page's frontmatter above the
layout chain, as Vue already does. React and Solid match contexts by
identity, so the adapter owns `FrontmatterContext` and the `@void/md`
runtime re-exports it. Svelte sets the context in `App.svelte`.
Fixes #451
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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Oct 18, 2026
Follow-up to #475. Since #475, an island on a Markdown page sees the page frontmatter through `useFrontmatter()` during server rendering, but `{}` in the browser. React, Svelte and Vue then report a hydration mismatch and re-render the island with `{}`. Vue islands had the same gap before #475. ``` server: island renders useFrontmatter().title → "Hello" browser: island hydrates as its own root, no page context → {} → mismatch, shows "undefined" ``` ## Behavior `useFrontmatter()` now returns the page's frontmatter everywhere on a Markdown page: layouts, the page, and islands, both on the server and in the browser. - A page that renders at least one island and has frontmatter includes it once: `<script type="application/json" id="__void_frontmatter">`. Pages without islands or without frontmatter send nothing new. - `initIslands` reads it and passes it to each adapter's island hydration, which provides it the same way the server does: React and Solid `FrontmatterContext`, the Svelte `hydrate()` context, Vue `provide`. - React and Solid load `@void/react` / `@void/solid` for this only when the page has frontmatter. - The Markdown guide now says islands can read it, and that frontmatter on pages with islands is visible in the HTML. ### Why send it, instead of giving islands `{}` Astro, îles and Fresh islands get only their props. Here, though, `useFrontmatter()` already works in layouts and pages. If islands silently got `{}`, users would fall into the same trap as #451. Frontmatter is already public through `@void/md/pages`, and the cost is one small JSON script on pages with islands. ## Tests - A browser test per adapter (`md-layout-frontmatter.test.ts` for React, Solid and Svelte, and the new `md-island-frontmatter.test.ts` for Vue) uses a shared helper, `test/island-page-browser.ts`. An island layout loads an island that prints `useFrontmatter().title`. Each test checks the JSON script is in the server HTML, then that the island still shows the title after hydration with no hydration warning. - Mutation checks: removing the browser-side provider for any one adapter makes its test show `undefined`. Removing the server script fails all four. - The #475 layout tests now also check that a page without islands gets no frontmatter script. - `islandFrontmatterScript` escapes `</script>` inside frontmatter values (`deferred-xss.test.ts`). - Run locally against the installed Chrome, because the Playwright Chromium download is blocked here. The existing `react-island-hydration` test still passes. Unit tests for void, md and the four adapters, lint, format and typecheck all pass. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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Fixes #451.
useFrontmatter()in a layout that wraps a.mdpage returned{}with React, Solid and Svelte. The frontmatter was provided only inside the page component, below its layouts. Vue already provided it at the app root.FrontmatterContext(next toSharedContext), and the@void/mdruntime re-exports it, souseFrontmatter()and the island renderer use the same context. The renderer does not import@void/md, so apps without it are unchanged.App.svelte, which sets the__void_frontmattercontext above the layouts.FrontmatterContext/setFrontmatter()exports of@void/mdare unchanged.Tests
packages/{react,solid,svelte}/test/integration/md-layout-frontmatter.test.ts): a layout printsuseFrontmatter().titlearoundindex.md. Onmainit renders<p id="fm"></p>; with the fix,<p id="fm">Hello from frontmatter</p>.@void/mdruntime create its own context again, fails that adapter's test.build+preview: root, nested and named layouts all show the page's frontmatter. Pages without frontmatter, plain pages and.islandpages still render.Known limits (unchanged by this PR)
useFrontmatter()still gets{}in the browser, because islands hydrate without page context.🤖 Generated with Claude Code