feat: migrate API routes to TypeScript

[devin-ai-integration]

Summary

Migrates pages/api/hello.js and pages/api/stripe.js from JavaScript to TypeScript, and sets up the TypeScript foundation for the project.

TypeScript setup:

• Added tsconfig.json with strict: true, allowJs: true (to coexist with remaining JS files)
• Added next-env.d.ts (auto-generated by Next.js)
• Added shared type definitions in types/index.ts (SanityProduct, CartItem, SanityBanner)
• Installed typescript, @types/react@17.0.39, @types/react-dom@17.0.11, @types/node

Babel removal:

• Removed .babelrc and uninstalled @babel/core + @babel/preset-react — Next.js 12's built-in SWC compiler handles JSX transformation

API route migrations:

• hello.ts: Added NextApiRequest/NextApiResponse typing to handler
• stripe.ts: Typed handler params, added CartItemBody interface for req.body.map(), typed params as Stripe.Checkout.SessionCreateParams, typed error in catch block

Review & Testing Checklist for Human

• Stripe apiVersion change: The original JS code called new Stripe(key) without an API version. The TS migration now explicitly passes { apiVersion: '2020-08-27' } (required by the Stripe v8 types). Verify this matches the version your Stripe account expects — if your account uses a different default API version, this could subtly change Stripe API behavior.
• Babel removal: .babelrc and Babel packages are removed in favor of Next.js SWC. If any other part of the build pipeline or tooling relied on Babel, this could break. Run the full app locally and test checkout flow end-to-end.
• NEXT_PUBLIC_STRIPE_SECRET_KEY! non-null assertion: The env var access uses ! — the app will throw at runtime if this var is missing. Consider whether a startup check or fallback would be safer.
• CartItemBody vs CartItem: stripe.ts defines its own CartItemBody interface rather than reusing CartItem from types/index.ts. The shapes differ (CartItemBody.image is typed as { asset: { _ref: string } }[] while CartItem.image is any[]). Verify CartItemBody matches what the frontend actually sends in the request body.

Recommended test plan: Start the dev server, add items to cart, complete a Stripe checkout flow, and confirm the /api/stripe endpoint still creates sessions correctly.

Notes

• @types/react is pinned to 17.0.39 because newer 17.x patches added an exports field that breaks Next.js 12's require.resolve('@types/react/index.d.ts') check during build.
• tsconfig.json includes "ignoreDeprecations": "6.0" because typescript@6.0.3 deprecates moduleResolution: "node".
• npx tsc --noEmit and npm run build both pass cleanly.

Link to Devin session: https://app.devin.ai/sessions/2aff6d8e68fb4c6fb96f729410bec23d
Requested by: @WesternConcrete

---

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 3 additional findings.

[devin-ai-integration]

Testing Results

Ran dev server locally and tested all migrated API routes end-to-end.

API Route Tests (4/4 passed)

Test	Result
GET /api/hello returns {"name":"John Doe"}	✅ Passed
GET /api/stripe returns 405 Method Not Allowed	✅ Passed
POST /api/stripe with cart item body reaches Stripe API	✅ Passed (400 from Stripe — expected, hardcoded shipping_rate doesn't exist in test account)
Homepage renders correctly after Babel removal	✅ Passed

Evidence

/api/hello

Homepage (Babel removal regression check)

/api/stripe shell output

# GET → 405
$ curl -s -o /dev/null -w "%{http_code}" http://localhost:3000/api/stripe
405

# POST → 400 (Stripe API error, not a runtime crash)
$ curl -s -X POST http://localhost:3000/api/stripe ...
No such shipping rate: 'shr_1Kn3IaEnylLNWUqj5rqhg9oV'
HTTP_STATUS:400

Devin session