fix(frontend): guard against SSR/hydration mismatch in theme provider - #1158
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omoh5 wants to merge 1 commit into
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fix(frontend): guard against SSR/hydration mismatch in theme provider#1158omoh5 wants to merge 1 commit into
omoh5 wants to merge 1 commit into
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…LabsCrypt#1083) Add blocking inline script in <head> that reads localStorage theme preference before first paint, preventing flash-of-wrong-theme when client theme differs from server-rendered default. Add comprehensive JSDoc comments documenting the SSR/hydration strategy in both theme-provider.tsx and layout.tsx.
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Summary
Closes #1083
This PR adds a blocking inline script that reads the user's stored theme preference from
localStorageand applies thedarkclass to<html>before the browser paints a single pixel. This prevents the flash-of-wrong-theme (FART) when the server renders a default theme class that differs from the user's persisted preference.Problem
theme-provider.tsxwrapsnext-themes'ThemeProvider, which runs as a client component. In Next.js 16 + React 19, the script injected bynext-themesvia portal may not be truly blocking — it runs after React hydrates, causing:lightand the server rendersdark, the browser paints dark first, then swaps to light.darkclass on<html>than what the server produced.Solution
Two-part approach inside
layout.tsx:<script>in<head>— readsflowfi-themefrom localStorage and synchronously adds/removes thedarkclass on<html>before the first paint. Handlesdark,light, andsystem(viamatchMedia) preferences. No flicker occurs because the correct class is present from the very first rendered frame.suppressHydrationWarningon<html>(already present) — tells React to skip the hydration-difference check for this element because we intentionally mutate its class list before hydration.Added comprehensive documentation:
theme-provider.tsx: Full JSDoc block explaining the SSR/hydration strategy and all configuration options.layout.tsx: Inline comments explaining both thesuppressHydrationWarningand the blocking script.Files Changed
frontend/src/context/theme-provider.tsxfrontend/src/app/layout.tsx<script>in<head>; updated commentsTesting
tsc --noEmit— no new errorsManual Verification
To reproduce the original issue:
lightin settings