Skip to content

fix: resolve flash of unstyled content in dark mode #766

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
TusharThakur04 wants to merge 1 commit into
base: main
Choose a base branch
from
+51 −3
Open

fix: resolve flash of unstyled content in dark mode #766

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
10 changes: 9 additions & 1 deletion src/generators/web/generate.mjs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,15 @@ import { writeFile } from '../../utils/file.mjs';
export async function generate(input) {
const config = getConfig('web');

const template = await readFile(config.templatePath, 'utf-8');
let template = await readFile(config.templatePath, 'utf-8');

// Read the theme script from UI folder
const themeScriptPath = join(import.meta.dirname, 'ui', 'theme-script.mjs');
const themeScriptContent = await readFile(themeScriptPath, 'utf-8');
Copy link
Copy Markdown
Member

@ovflowd ovflowd Apr 16, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

We shouldn't ue fs the idea is to use our rolldown pipeline for this script, so it gets properly minified and transformed.

Copy link
Copy Markdown
Member

@ovflowd ovflowd Apr 16, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Otherwise the file doesn't get minified, which is the idea behind separating src<>final result.


// Wrap theme script in script tag and replace the placeholder
const inlinedThemeScript = `<script>${themeScriptContent}</script>`;
template = template.replace('${themeScript}', inlinedThemeScript);
Copy link
Copy Markdown
Member

@ovflowd ovflowd Apr 16, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Don't use .replace(), I believe that @avivkeller implemented a system to automatically evaluate such template variables?


// Process all entries: convert JSX to HTML/CSS/JS
const { results, css, chunks } = await processJSXEntries(input, template);
Expand Down
8 changes: 6 additions & 2 deletions src/generators/web/template.html
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -18,8 +18,12 @@
<link rel="stylesheet"
href="https://fonts.googleapis.com/css2?family=IBM+Plex+Mono&family=Open+Sans:ital,wght@0,300..800;1,300..800" />

<!-- Apply theme before paint to avoid Flash of Unstyled Content -->
<script>document.documentElement.setAttribute("data-theme", document.documentElement.style.colorScheme = localStorage.getItem("theme") || (matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light"));</script>
<!--
Copy link
Copy Markdown
Member

@ovflowd ovflowd Apr 16, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

No need for this comment.

This placeholder is dynamically replaced by generator.mjs.
It injects an inline script that initializes the theme (light/dark)
before the page renders to avoid Flash of Unstyled Content (FOUC).
-->
${themeScript}
Copy link
Copy Markdown
Member

@ovflowd ovflowd Apr 16, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
${themeScript}
<script type="javascript">${themeScript}</script>

<script type="importmap">${importMap}</script>
<script type="speculationrules">${speculationRules}</script>
</head>
Expand Down
36 changes: 36 additions & 0 deletions src/generators/web/ui/theme-script.mjs
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,36 @@
'use strict';

/**
* This script is designed to be inlined in the <head> of the HTML template.
* It must execute BEFORE the body renders to prevent a Flash of Unstyled Content (FOUC).
*/
(function initializeTheme() {
const THEME_STORAGE_KEY = 'theme';
const THEME_DATA_ATTRIBUTE = 'data-theme';
const DARK_QUERY = '(prefers-color-scheme: dark)';

// 1. Retrieve the user's preference from localStorage
const savedUserPreference = localStorage.getItem(THEME_STORAGE_KEY);

// 2. Determine if the system/browser is currently set to dark mode
const systemSupportsDarkMode = window.matchMedia(DARK_QUERY).matches;

/**
* 3. Logic to determine if 'dark' should be applied:
* - User explicitly saved 'dark'
* - User set preference to 'system' AND system is dark
* - No preference exists yet AND system is dark
*/
const shouldApplyDark =
savedUserPreference === 'dark' ||
(savedUserPreference === 'system' && systemSupportsDarkMode) ||
(!savedUserPreference && systemSupportsDarkMode);

const themeToApply = shouldApplyDark ? 'dark' : 'light';

// 4. Apply the theme attribute to the document element (<html>)
document.documentElement.setAttribute(THEME_DATA_ATTRIBUTE, themeToApply);

// 5. Set color-scheme to ensure browser UI (scrollbars, etc.) matches the theme
document.documentElement.style.colorScheme = themeToApply;
})();
Loading