Astro Starlight 0.42: Popover mobile menu + JS distribution (2 Sep 2026)

On 2 September 2026, Astro published Starlight 0.42—the official documentation theme—with a Popover-based mobile menu, a packaging change from TypeScript source to compiled JavaScript plus .d.ts files, and several breaking minimums. ShopperCove did not upgrade a production Starlight site for this note. Package identity was confirmed on npm on 5 October 2026 (@astrojs/starlight@0.42.5, dist-tag latest; 0.42.0 published 2026-09-02T11:13:45.169Z). Primary sources: the Starlight 0.42 blog post, the GitHub release @astrojs/starlight@0.42.0, and the Starlight docs site. This is a docs-based upgrade checklist—not performance advice and not a security advisory.

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Headline changes in 0.42.0

From the blog and release notes:

Upgrade path recommended by Astro:

npx @astrojs/upgrade

Patches through 0.42.5 (npm latest)

As of sources read 5 Oct 2026, npm latest is 0.42.5 (published 1 Oct 2026). Notable patches after 0.42.0 (from GitHub releases):

• 0.42.1 — desktop sidebar popover attribute fix
• 0.42.3 — TOC highlighting freeze guard when #_top is missing
• 0.42.4 — large nested sidebar render optimization; icon fixes
• 0.42.5 — Macedonian language support

Pin @astrojs/starlight@0.42.5 (or current latest) when you upgrade; keep Astro on the 7.2.10+ line the release requires.

Hands-on upgrade checklist

1. Inventory: note current @astrojs/starlight and astro versions (npm ls @astrojs/starlight astro).
2. Upgrade together: run npx @astrojs/upgrade (or pin Starlight 0.42.5 + Astro ≥7.2.10). Confirm with npm view @astrojs/starlight version → expect 0.42.5 as of 5 Oct 2026.
3. Config cleanup: remove any tagline key from the Starlight config object.
4. Custom CSS / overrides: if you styled starlight-menu-button, [aria-expanded], or [data-mobile-menu-expanded], rewrite to .sl-menu-button and :popover-open / body:has(sl-sidebar-pane:popover-open) per the release notes.
5. Smoke-test mobile menu with JS disabled in DevTools — the Popover path is a deliberate reliability win.
6. Do not invent security urgency: this minor is features + packaging + a11y/perf; ShopperCove is not attaching CVE IDs.

ShopperCove did not change production Starlight versions for this article. Prefer the official blog and GitHub release over third-party roundups. For the Astro framework line already covered on ShopperCove, see the live Astro 7.3 preview note—this package is the Starlight docs theme.

Bottom line

Starlight 0.42 (2 Sep 2026; npm latest 0.42.5 on 1 Oct) brings a Popover mobile menu, JS+d.ts distribution, and Astro 7.2.10+ / modern-browser minimums. Upgrade with @astrojs/upgrade, drop tagline, and re-check custom menu CSS. No affiliate.

Sources

• https://astro.build/blog/starlight-042/
• https://github.com/withastro/starlight/releases/tag/%40astrojs/starlight%400.42.0
• https://github.com/withastro/starlight/releases/tag/%40astrojs/starlight%400.42.5
• https://registry.npmjs.org/@astrojs/starlight/0.42.5
• https://starlight.astro.build/
• https://github.com/withastro/starlight/blob/main/packages/starlight/CHANGELOG.md

Related

• https://www.shoppercove.com/blog/astro-7-3-preview-ignore-lock-october-2026
• https://www.shoppercove.com/blog/eslint-10-12-release-october-2026
• https://www.shoppercove.com/blog/vite-plus-1-0-unified-toolchain-october-2026
• https://www.shoppercove.com/blog/playwright-1-63-test-locks-october-2026
• https://www.shoppercove.com/blog/angular-router-ssr-queryparams-dos-october-2026
• https://www.shoppercove.com/blog/webpack-5-111-esm-output-stable-september-2026
• https://www.shoppercove.com/blog/nodejs-26-lts-october-2026-schedule-change
• https://www.shoppercove.com/blog/nextjs-15-lts-end-of-support-october-2026