How does Next.js handle TypeScript support?

TypeScript is a first-class citizen in Next.js — zero config, recommended for new projects, and integrated deeply enough that the framework itself publishes types for its APIs.

Starting a TypeScript project is just a flag:

npx create-next-app@latest my-app --typescript

You get tsconfig.json, next-env.d.ts, and .tsx extensions on every scaffolded file. On an existing JavaScript project, rename a file to .ts or .tsx and run next dev — Next.js auto-installs TypeScript and generates the config.

What Next.js gives you out of the box:

• Preconfigured tsconfig — strict mode on, JSX set to preserve, path aliases like @/* ready to use.

• next-env.d.ts — ambient types for Next.js-specific globals. Don't edit this file; Next regenerates it on each dev start.

• Typed routes — with experimental.typedRoutes: true, Link href=... only accepts valid route strings. Typos fail at compile time.

• Typed component APIs — AppProps, GetStaticProps, GetServerSideProps, NextApiRequest, NextApiResponse, Metadata, and generateStaticParams all ship with rich types.

• Server Component typing — async server components get correct return type inference. Server actions can be typed end-to-end.

• Build-time type checking — next build runs tsc --noEmit and fails the build on type errors. Disable with typescript.ignoreBuildErrors: true in config (not recommended).

Under the hood, Next uses SWC (and optionally Turbopack) to transpile TypeScript at full speed. It doesn't use tsc to emit code — tsc is only run for type checking. That means TypeScript-specific features tsc would transform (namespaces, enums in some modes) work through SWC with matching behavior.

Patterns that work well:

• Typed fetchers — wrap fetch with a generic to keep response types narrow across Server Components.

• Zod for runtime + compile time — define a Zod schema for form or API payloads and infer the TypeScript type from it so the two never drift.

• Strict mode in tsconfig — always. The framework scaffolds it on by default.

• Generated types for routes — .next/types/ contains types Next writes after each build; add it to include in tsconfig.json (the scaffolded config does this).

One gotcha: dev mode type errors show in the terminal but don't fail page loads. Run tsc --noEmit --watch alongside next dev (or use your editor) to catch them as you type.