Sandbox::https://github.com/uswds/uswds/pull/6715

ericsorenson · 2026-06-17T17:41:46Z

Upgrades Storybook from 8.6 to 9.1 and migrates the build pipeline from Webpack to Vite. Storybook 9 removed @storybook/html-webpack5, so this migrates the framework to @storybook/html-vite. Because USWDS renders Twig templates client-side and ships component JavaScript as CommonJS, two custom Vite plugins were written to preserve existing behavior without modifying component source files.

What changed

Framework & dependencies

Upgraded storybook 8.6 → 9.1.20
Replaced @storybook/html-webpack5 with @storybook/html-vite
Removed @storybook/addon-essentials (controls, viewport, backgrounds, actions are now built into Storybook 9 core)
Bumped @storybook/addon-a11y and @storybook/test-runner (0.21 → 0.23) to SB9-compatible versions
Removed now-unused Webpack loaders: css-loader, file-loader, postcss-loader, resolve-url-loader, sass-loader, style-loader

New build tooling (tasks/)

vite-plugin-twig.mjs — compiles .twig templates into ESM render functions; resolves @components/@templates namespace aliases and {% include %}, {% extends %}, {% embed %}, {% from %}, {% import %} dependencies; cascades HMR through the template dependency graph
vite-plugin-uswds-cjs.mjs — transforms USWDS component CJS (require/module.exports) into ESM at build time (with source maps via MagicString), avoiding a Rollup commonjs-plugin crash on the circular uswds-core dependency graph
twig-esm-wrapper.mjs — provides ESM-compatible named exports for the CJS-only twig package in production builds

Configuration

.storybook/main.js — rewritten for html-vite with a viteFinal hook (Twig plugin, CJS plugin, SCSS asset-path overrides, optimizeDeps, resolve aliases)
.storybook/preview.js — updated a11y parameter from deprecated a11y.manual to a11y.test.disable

Notes / out of scope

The separate build:html Webpack pipeline (webpack.twig.config.js, tasks/webpack-twig-loader.js) is unchanged
.storybook/main.js remains CommonJS because Storybook 9 loads config via esbuild-register, which cannot evaluate native ESM config files (this is resolved in Storybook 10)
CSF2 → CSF3 story migration is intentionally deferred to a separate PR to keep this diff focused on the framework migration

How to Test

Check out this branch and run a clean install:
```
npm install
```
Dev server — start Storybook and confirm it boots on html-vite:
```
npm start
```
- Storybook should report Storybook 9.1.20 for html-vite started
- Open localhost:6006 and verify the sidebar shows all categories: Design Tokens, Components, Patterns, Pages
Verify rendering across template patterns — open and confirm each renders with full USWDS styling and no console errors:
- Simple template: Components → Alert → Default
- {% include %}: Components → Header → Default
- {% from %} macros: Components → Pagination → Default
- {% embed %} blocks: Components → Footer → Big Footer
Verify interactive JS components work (toggle/open behavior):
- Accordion (expand/collapse), Date Picker (calendar opens), Combo Box (dropdown opens), Modal (opens on trigger)
HMR — with the dev server running, edit a .twig file and confirm the story updates
Production build — confirm the static build succeeds:
```
npm run build:storybook
```
Accessibility tests — confirm the a11y suite passes against the built output:
```
npm run test:a11y
```
Confirm the separate HTML build is unaffected:
```
npm run build:html
```

github-actions · 2026-06-23T00:20:58Z

✅ All commits on this PR have a verified signature. Thanks!

ericsorenson · 2026-06-24T00:05:28Z

Hi @ericsorenson — thanks for your contribution!

There is one thing that may be holding this up: for security reasons, USWDS requires that all commits to this repo have a verified commit. The following commit(s) on this PR aren't verified:

2dcf683 — updating contributors list

c0aa47e — fix: add role=presentation to contributors table and update contributor count

Here's what's needed:
Set up signature verification in GitHub. Use one of the following GitHub guides to set up your verification signature:

GPG commit signature verification

SSH commit signature verification
Rebase your commits with your verified signature. Once your signature is set up, complete the following steps in the terminal to update the verification status of your previous commits:
git checkout feat/storybook-9-upgrade
git rebase origin/develop
git push --force-with-lease
Please let us know if you have any questions. We appreciate your help here. This comment will update automatically once your commits are verified.

These aren't commits from me?

ethangardner · 2026-06-24T01:30:46Z

@ericsorenson - You're right. I'm not sure what happened there. There's an open issue with the workflow (bot) that created the commits, and it's paused until we get it sorted out. Would you mind rebasing and dropping those commits? You can force push with the --force-with-lease flag once those bot commits are dropped. We can pair on it if you'd like to get it figured out together. I'll message you.

Replace the previous CJS-wrapper approach with an esbuild-bundled virtual twig runtime to provide reliable CJS→ESM interop in both dev and production. - Removed tasks/twig-esm-wrapper.mjs (no longer needed). - Updated tasks/vite-plugin-twig.mjs: - Add esbuild buildSync to pre-bundle the twig package into a single ESM virtual module (virtual:uswds-twig-runtime) and serve it via load(). - Use the bundled default export (Twig) in generated .twig module transforms instead of importing { twig } from the raw CJS package. - Lazy-cache the bundle and stub Node built-ins in the esbuild bundle. - Removed logic that redirected to the old wrapper and removed isBuild flag usage. - Updated .storybook/main.js to remove the previous optimizeDeps "twig" pre-bundle and Rollup commonjsOptions workaround, since the plugin now handles bundling. - Minor security/performance fix in tasks/vite-plugin-uswds-cjs.mjs: tighten the regex used for CJS destructure detection to avoid catastrophic backtracking (ReDoS) and added an explanatory comment. These changes fix runtime failures caused by Rollup/@rollup/plugin-commonjs failing to statically analyze twig's internal require graph and unify behavior across dev and build.

ericsorenson · 2026-06-29T13:28:20Z

@ericsorenson - You're right. I'm not sure what happened there. There's an open issue with the workflow (bot) that created the commits, and it's paused until we get it sorted out. Would you mind rebasing and dropping those commits? You can force push with the --force-with-lease flag once those bot commits are dropped. We can pair on it if you'd like to get it figured out together. I'll message you.

This should be good to go.

ethangardner · 2026-06-29T18:20:17Z

Thanks, @ericsorenson. I'm teeing this one up for review. I'll give you input within the next day or two.

ethangardner

Thanks for the contribution! I appreciated the comments you added throughout. They made it much easier for me to review. I like the general approach here. There were some questions and changes I had in this but this is overall a very solid start.

Update Storybook SCSS comments and remove forced asset path overrides so USWDS relative $theme-image-path/$theme-font-path resolve correctly when Storybook is served from non-root paths. Rewrite the CJS->ESM plugin transform for `const { ... } = require(...)`: replace an error-prone multi-line regex with a linear index-scan that finds destructure openers, matches the closing brace, validates the body, and rewrites to `import _modN` + destructure. This avoids ReDoS risks, handles multi-line patterns reliably, and cleans up formatting and residual-CJS warnings.

Replace synchronous buildSync with async build to enable proper promise caching for concurrent bundling. Cache the bundling promise (not the resolved value) so concurrent load() calls dedupe onto a single esbuild run. Add stubNodeBuiltins esbuild plugin to resolve Node built-ins (fs, path, module) to empty modules, preventing console warnings from twig's try/catch error handling.

Add build-tooling tests for repo tasks. tasks/test.js introduces tasksTests() to run ESM specs in tasks/**/*.spec.mjs; gulpfile.js exports tasksTests and includes it in the main test series; package.json adds an npm script "test:tasks". Adds a new spec tasks/vite-plugin-uswds-cjs.spec.mjs that verifies the CJS→ESM Vite plugin transforms (including skip rules and ReDoS regression checks).

Add esbuild to package.json and package-lock.json. Add new unit tests at tasks/vite-plugin-twig.spec.mjs that cover the Vite Twig plugin's resolveId, transform, and load hooks (including ensuring the bundled runtime has no throwing require("fs") shim). Run with: npm run test:tasks.

ethangardner

Thanks, @ericsorenson! I spotted one issue for HMR that I uncovered in testing and added the steps to reproduce that. If you can resolve that, I think we'll be all set here.

Looking at the cjs plugin you wrote, I'm going to suggest a follow up PR once and issue so we can remove the UMD-related checks from the plugin. There's only 1 UMD file in the repo at this point, and I think that'll help us dial down the complexity for things we're adding. I'll create the issue for it and hold off on doing it so you're not dealing with conflicts or things changing while this work is in progress.

Move `Twig.cache(false)` from the build-time Node instance to the bundled browser runtime. The Node-side instance is only used to compile .twig source files; the browser runtime is what actually executes templates and registers ids. Without cache disabled on the bundled runtime, HMR re-execution of a .twig module throws "There is already a template with the ID" when re-registering the template. Inject cache disabling into the bundled runtime via regex substitution. Add ESLint support for .spec.mjs files and end-to-end tests verifying HMR re-registration works.

Turn off Twig's Node-side cache during build/HMR by calling Twig.cache(false). During HMR, transform() re-runs Twig.twig({ id, data }) on the build-time instance; with caching enabled re-registering a template id throws "There is already a template with the ID …". Add a comment explaining the rationale.

…-upgrade

ethangardner

Thanks for the strong work on this and working through the issues. Thanks for your patience waiting for me to get this reviewed. This is ready to go and looks good to me!

github-project-automation Bot added this to USWDS Core Project Data Jun 17, 2026

github-project-automation Bot moved this to Triage in USWDS Core Project Data Jun 17, 2026

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ericsorenson marked this pull request as ready for review June 17, 2026 18:38

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ethangardner mentioned this pull request Jun 24, 2026

USWDS - Contributors: Rewrite workflow to use signed commits and single-step table generation #6733

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ericsorenson force-pushed the feat/storybook-9-upgrade branch 2 times, most recently from a725e7e to 7f07019 Compare June 25, 2026 17:21

ericsorenson added 2 commits June 25, 2026 12:24

Storybook: Upgrade to Storybook 9 and migrate from Webpack to Vite

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ericsorenson force-pushed the feat/storybook-9-upgrade branch from 7f07019 to 64af115 Compare June 25, 2026 17:24

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Merge branch 'develop' into feat/storybook-9-upgrade

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chandracarney added the Storybook Work on component stories, previews, or the Storybook development environment. label Jun 30, 2026

ethangardner moved this from Triage to Peer Review in USWDS Core Project Data Jun 30, 2026

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Merge branch 'develop' into feat/storybook-9-upgrade

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Merge branch 'develop' into feat/storybook-9-upgrade

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Comment thread tasks/vite-plugin-twig.mjs Resolved

Comment thread tasks/vite-plugin-twig.mjs Resolved

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Comment thread tasks/vite-plugin-twig.mjs Resolved

Comment thread .storybook/main.js Resolved

ethangardner moved this from In progress to Initial Fed Review in USWDS Core Project Data Jun 30, 2026

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ericsorenson added 3 commits July 6, 2026 08:59

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Merge branch 'develop' into feat/storybook-9-upgrade

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USWDS Core - Update sanitizer.js to modern syntax #6752

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ericsorenson added 2 commits July 10, 2026 16:02

Merge branch 'develop' into feat/storybook-9-upgrade

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ethangardner mentioned this pull request Jul 15, 2026

USWDS - Core: Convert sanitizer.js to CommonJS and fix falsy-value bug #6760

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ethangardner added this to the uswds 3.14.0 - Aug 2026 milestone Aug 4, 2026

This was referenced Aug 11, 2026

USWDS - Draft 3.14.0 release notes #6809

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USWDS Release 3.14.0 #6822

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USWDS - JS: Migrate CommonJS to ECMAScript Modules (Stage 1: zero consumer-visible change) #6845

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USWDS - Storybook: Upgrade to Storybook 9 and migrate from Webpack to Vite - #6715

USWDS - Storybook: Upgrade to Storybook 9 and migrate from Webpack to Vite#6715
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ericsorenson commented Jun 17, 2026

What changed

How to Test

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