How does Next.js handle TypeScript support?

Question

Accepted Answer

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. Highlight that Next.js auto-installs TypeScript dependencies and generates tsconfig.json — zero manual configuration. Mention the next-env.d.ts file. This question tests whether you have actually set up TypeScript in Next.js.