Mastering TypeScript in Next.js: From Basics to Advanced Patterns

TypeScript has become the gold standard for building scalable, maintainable web applications. When combined with Next.js, it provides an unbeatable developer experience — combining type safety with server-side rendering and edge-ready performance.

1. Why TypeScript in Next.js?

JavaScript is flexible, but flexibility can lead to runtime errors. TypeScript adds static type checking, catching bugs before they reach production. In large codebases, this means fewer surprises and faster refactors.

Example:

type User = { id: number; name: string; email?: string; };

function greet(user: User) { return Hello, ${user.name}!; }

2. Setting Up TypeScript in Next.js

You don’t have to start from scratch. Just install the dependencies:

npm install typescript @types/react @types/node --save-dev

Then run your development server:

npm run dev

Next.js will automatically create a tsconfig.json for you.

3. Common Patterns

Type your API routes using NextApiRequest and NextApiResponse.

Use utility types like Partial, Pick, and Omit to transform interfaces easily.

Leverage Generics for reusable hooks and components.

Example:

function useFetch<T>(url: string): [T | null, boolean] { const [data, setData] = useState<T | null>(null); const [loading, setLoading] = useState(true);

useEffect(() => { fetch(url) .then((res) => res.json()) .then((json) => setData(json)) .finally(() => setLoading(false)); }, [url]);

return [data, loading]; }

4. Type-Safe API Routes with tRPC

tRPC eliminates the need for manual API typing — your backend and frontend share the same type definitions. This ensures end-to-end type safety without GraphQL overhead.

Example:

const postRouter = createTRPCRouter({ create: publicProcedure .input(z.object({ title: z.string(), content: z.string() })) .mutation(async ({ input }) => { return prisma.post.create({ data: input }); }), });

5. Advanced Tips

Always use as const for fixed objects.

Prefer discriminated unions for handling multiple states.

Combine Zod with TypeScript to validate both at runtime and compile time.

Example:

const userSchema = z.object({ id: z.number(), name: z.string(), });

type User = z.infer<typeof userSchema>;

6. Conclusion

By combining Next.js and TypeScript, you create a development environment that’s fast, reliable, and maintainable. Once you start typing your code, you’ll never want to go back.