TypeScript Integration

TypeScript is a superset of JavaScript that adds static type definitions. Next.js provides an integrated, out-of-the-box TypeScript experience right from the start. In modern workflows, writing Next.js apps with TypeScript is highly recommended to catch bugs before runtime.

Adding TypeScript to an Existing Project

If you created your app without TypeScript initially, it is extremely easy to convert. Simply create an empty `tsconfig.json` file in your root folder:

touch tsconfig.json

Then, start your development server:

npm run dev

Next.js will detect the file, recognize that you are missing dependencies, and prompt you to install them:

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

Once installed, Next.js automatically populates the `tsconfig.json` with the optimal compiler settings for Next.js.

Typing React Components

With TypeScript enabled, you can define prop interfaces for your components to prevent incorrect data from being passed.

// components/Button.tsx
type ButtonProps = {
  text: string;
  onClick: () => void;
  disabled?: boolean; // Optional prop
};

export default function Button({ text, onClick, disabled = false }: ButtonProps) {
  return (
    <button onClick={onClick} disabled={disabled}>
      {text}
    </button>
  );
}

Typing Route Handlers (API Routes)

Next.js provides native types for requests and responses, so you have complete IntelliSense for HTTP headers, cookies, and JSON bodies.

// app/api/users/route.ts
import { NextResponse, NextRequest } from 'next/server';

type UserData = {
  name: string;
  age: number;
};

export async function POST(request: NextRequest) {
  // body is automatically typed as UserData
  const body: UserData = await request.json();

  if (body.age < 18) {
    return NextResponse.json({ error: "Too young" }, { status: 400 });
  }

  return NextResponse.json({ success: true, name: body.name });
}

Conclusion

Combining Next.js Server Components, Server Actions, aggressive Static Caching, and strict TypeScript types equips you with arguably the most powerful stack in the entire React ecosystem today. This completes your deep dive into Next.js architecture!