Introduction

This tutorial aims to guide you in exploring the TypeScript features available in Next.js. TypeScript is a very powerful tool that can help you write more robust, error-free code by adding static types to JavaScript, which allows you to catch errors early in the development process.

By the end of this tutorial, you will learn:

• How to set up a Next.js project with TypeScript
• How to use TypeScript types and interfaces in your Next.js project
• Best practices when using TypeScript with Next.js

Prerequisites: Basic knowledge of JavaScript and React will be beneficial. Familiarity with Next.js is not required but could be helpful.

Step-by-Step Guide

Setting up a New Next.js Project with TypeScript

1. To create a new Next.js project with TypeScript, you can use create-next-app with the --example with-typescript flag:

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

1. This command will create a new Next.js project with a tsconfig.json file, which is used for configuring TypeScript compiler options, and a next-env.d.ts file, which tells TypeScript to include type definitions from Next.js.

Using TypeScript Types and Interfaces in Next.js

1. In your Next.js pages or components, you can define props using TypeScript interfaces:

interface Props {
  name: string;
  age: number;
}

function Profile({ name, age }: Props) {
  return (
    <div>
      <p>{name}</p>
      <p>{age}</p>
    </div>
  );
}

1. You can also use TypeScript types for your data fetching methods like getStaticProps, getServerSideProps, or getInitialProps.

import { GetServerSideProps } from 'next';

interface Props {
  posts: Post[];
}

export const getServerSideProps: GetServerSideProps<Props> = async () => {
  const res = await fetch('https://api.example.com/posts');
  const posts: Post[] = await res.json();

  return {
    props: {
      posts,
    },
  };
};

Code Examples

Example 1: TypeScript with Next.js Pages

// pages/index.tsx

import { GetStaticProps } from 'next';

interface Post {
  id: string;
  title: string;
}

interface IndexProps {
  posts: Post[];
}

const IndexPage = ({ posts }: IndexProps) => (
  <div>
    {posts.map((post) => (
      <div key={post.id}>
        <h2>{post.title}</h2>
      </div>
    ))}
  </div>
);

export const getStaticProps: GetStaticProps<IndexProps> = async () => {
  const res = await fetch('https://api.example.com/posts');
  const posts: Post[] = await res.json();

  return {
    props: {
      posts,
    },
  };
};

export default IndexPage;

In this example, we're fetching posts from an API in getStaticProps and passing them as props to our page component. We're using the GetStaticProps type from Next.js to type the props and the return value of getStaticProps.

Example 2: TypeScript with Next.js API Routes

// pages/api/hello.ts

import { NextApiRequest, NextApiResponse } from 'next';

export default (req: NextApiRequest, res: NextApiResponse) => {
  res.status(200).json({ name: 'John Doe' });
};

In this example, we're typing the request and response objects in our API route using the NextApiRequest and NextApiResponse types from Next.js.

Summary

In this tutorial, we covered how to set up a Next.js project with TypeScript, how to use TypeScript types and interfaces in your Next.js pages and API routes, and some best practices to follow when using TypeScript with Next.js.

As next steps, you could explore more advanced TypeScript features and how to use them with Next.js, such as generics and utility types. You could also learn about how to set up a testing framework like Jest with TypeScript and Next.js.

Additional Resources:
- Next.js Documentation
- TypeScript Documentation

Practice Exercises

1. Create a Next.js page that fetches user data from an API and displays it. Use TypeScript types to define the user data structure.

2. Create a Next.js API route that accepts a POST request with a name and message in the request body. Use TypeScript to type the request body.

3. Modify the API route from exercise 2 to return an error response if the name or message is missing from the request body. Use TypeScript to ensure that the error response has a status and error property.

Solutions and explanations for these exercises, as well as tips for further practice, can be found on the official Next.js GitHub repo.