How to Use TypeScript with Next.js and the Benefits of Using TypeScript?

Maria
NextJs
10 Jul, 2024

TypeScript has gained significant popularity among developers due to its ability to catch errors at compile-time and its support for static typing. Integrating TypeScript into a Next.js project can significantly enhance the development experience by providing better tooling, type safety, and maintainability. This article will guide you through the process of setting up TypeScript in a Next.js project and highlight the benefits of using TypeScript.

Benefits of Using TypeScript in Next.js

Enhanced Developer Experience: TypeScript provides powerful tools such as IntelliSense, auto-completion, and inline documentation, which significantly improve the developer experience. These features help in writing code faster and with fewer errors.
Early Error Detection: With static typing, TypeScript catches errors at compile-time rather than at runtime. This early detection helps prevent many common errors, such as type mismatches, which can save time during the debugging process.
Improved Code Quality and Maintainability: TypeScript enforces type safety, making the code more predictable and easier to understand. This leads to higher code quality and makes it easier to maintain, especially in large codebases.
Better Refactoring: Refactoring code in TypeScript is safer and more reliable due to its type system. When you change a type definition, TypeScript will highlight all the places that need to be updated, reducing the risk of introducing bugs during refactoring.
Enhanced Collaboration: TypeScript’s explicit type definitions and interfaces make it easier for teams to understand and collaborate on a codebase. New developers can quickly understand the data structures and expected inputs/outputs of functions and components.
Seamless Integration with Next.js: Next.js has built-in support for TypeScript, which means you don’t need to configure much to get started. This seamless integration allows you to take advantage of TypeScript’s benefits without significant setup overhead.
Interoperability with JavaScript: TypeScript is a superset of JavaScript, which means you can gradually introduce it into an existing JavaScript codebase. This interoperability allows for a smooth transition to TypeScript without the need for a complete rewrite.

You can see this article on basic types in TypeScript and advanced types in TypeScript to understand all type before you start actually using them.

Also, you can our article on basic types in TypeScript and advanced types in TypeScript

Setting Up TypeScript in Next.js

Next.js provides first-class support for TypeScript, making it straightforward to set up and start using. Follow these steps to integrate TypeScript into your Next.js project:

Initial Project Setup

If you don't already have a Next.js project, create one using the create-next-app command. If you already have a project, skip to the next step.

npx create-next-app@latest my-nextjs-app
cd my-nextjs-app

Adding TypeScript to Your Project

Install TypeScript and Required Packages:

Install TypeScript and the necessary type definitions for React and Node.
```
npm install --save-dev typescript @types/react @types/node
```
Create a tsconfig.json File:

Next.js will automatically create a tsconfig.json file for you when you add your first TypeScript file. To manually create it, you can run:
```
npx tsc --init
```
Rename JavaScript Files to TypeScript:

Rename your .js files to .ts for regular files and .tsx for files containing JSX.
```
mv pages/index.js pages/index.tsx
```
Run the Development Server:

Start the development server. Next.js will automatically configure your project for TypeScript.
```
npm run dev
```
This will also generate a tsconfig.json file if it doesn’t exist.

TypeScript Configuration

Next.js provides a default tsconfig.json configuration, but you can customize it according to your needs. Here’s an example of a basic tsconfig.json:

{
  "compilerOptions": {
    "target": "es5",
    "lib": ["dom", "dom.iterable", "esnext"],
    "allowJs": true,
    "skipLibCheck": true,
    "strict": true,
    "forceConsistentCasingInFileNames": true,
    "noEmit": true,
    "esModuleInterop": true,
    "module": "esnext",
    "moduleResolution": "node",
    "resolveJsonModule": true,
    "isolatedModules": true,
    "jsx": "preserve"
  },
  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx"],
  "exclude": ["node_modules"]
}

Adding Type Definitions

TypeScript uses type definitions to provide type information about libraries and modules. For commonly used libraries, you can install type definitions from DefinitelyTyped.

For example, to add type definitions for popular libraries:

npm install --save-dev @types/react @types/react-dom

Creating a Typed Component

Now, let’s create a typed component to see TypeScript in action.

// pages/index.tsx

import { NextPage } from "next";

interface Props {
  title: string;
}

const Home: NextPage<Props> = ({ title }) => {
  return (
    <div>
      <h1>{title}</h1>
    </div>
  );
};

export default Home;

Use Case of Using TypeScript with Next.js

Project Overview

A company is developing a large-scale e-commerce platform using Next.js. The project involves multiple developers, frequent updates, and complex business logic. The team decides to integrate TypeScript to improve code quality, maintainability, and collaboration efficiency.

Challenges Addressed by TypeScript:

Complex Data Models: The platform deals with various complex data models, such as user profiles, product details, and order histories. Ensuring the accuracy of these data structures across the application is critical.
Frequent Changes and Feature Additions: The project undergoes frequent changes and additions of new features, increasing the risk of introducing bugs and breaking existing functionality.
Team Collaboration: Multiple developers are working on the project, requiring clear communication and consistent code quality to avoid conflicts and ensure smooth integration.

Implementation Steps:

Initial Setup: The team sets up TypeScript in their existing Next.js project by installing TypeScript and necessary type definitions.
```
npm install typescript @types/react @types/node
touch tsconfig.json
```

Define Data Models with TypeScript: The team defines interfaces for complex data models to ensure type safety and consistency across the application.

// models/Product.ts
export interface Product {
  id: string;
  name: string;
  description: string;
  price: number;
  inStock: boolean;
}

// models/User.ts
export interface User {
  id: string;
  name: string;
  email: string;
  role: "customer" | "admin";
  orderHistory: Order[];
}

// models/Order.ts
export interface Order {
  id: string;
  userId: string;
  productIds: string[];
  totalAmount: number;
  status: "pending" | "shipped" | "delivered";
}

Enhance Components and Pages with Type Safety: The team converts JavaScript components and pages to TypeScript, leveraging type annotations and interfaces to ensure type safety.

// components/ProductCard.tsx
import React from 'react';
import { Product } from '../models/Product';

interface ProductCardProps {
  product: Product;
}

const ProductCard: React.FC<ProductCardProps> = ({ product }) => (
  <div className="product-card">
    <h2>{product.name}</h2>
    <p>{product.description}</p>
    <p>${product.price}</p>
    <p>{product.inStock ? 'In Stock' : 'Out of Stock'}</p>
  </div>
);

export default ProductCard;

Type-Safe API Integration: The team ensures type-safe API integration by defining request and response types, reducing errors and improving development efficiency.

// services/api.ts
import { Product } from "../models/Product";
import { User } from "../models/User";

export const fetchProducts = async (): Promise<Product[]> => {
  const response = await fetch("/api/products");
  const products: Product[] = await response.json();
  return products;
};

export const fetchUser = async (userId: string): Promise<User> => {
  const response = await fetch(`/api/users/${userId}`);
  const user: User = await response.json();
  return user;
};

Custom Hooks with Generics: The team creates reusable custom hooks with generics to handle various data fetching scenarios, promoting code reuse and reducing boilerplate.

// hooks/useFetch.ts
import { useState, useEffect } from "react";

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

  useEffect(() => {
    const fetchData = async () => {
      try {
        const response = await fetch(url);
        const result: T = await response.json();
        setData(result);
      } catch (err) {
        setError(err.message);
      } finally {
        setLoading(false);
      }
    };

    fetchData();
  }, [url]);

  return [data, loading, error];
};

export default useFetch;

Testing with Type Safety: The team writes tests with type safety, ensuring the test cases align with the expected data structures and reducing runtime errors.

// tests/productCard.test.tsx
import React from 'react';
import { render } from '@testing-library/react';
import ProductCard from '../components/ProductCard';
import { Product } from '../models/Product';

const product: Product = {
  id: '1',
  name: 'Sample Product',
  description: 'This is a sample product',
  price: 19.99,
  inStock: true,
};

test('renders product card correctly', () => {
  const { getByText } = render(<ProductCard product={product} />);
  expect(getByText('Sample Product')).toBeInTheDocument();
  expect(getByText('This is a sample product')).toBeInTheDocument();
  expect(getByText('$19.99')).toBeInTheDocument();
  expect(getByText('In Stock')).toBeInTheDocument();
});

Benefits Achieved:

Reduced Errors: Static type checking catches errors at compile-time, reducing runtime errors and improving code reliability.
Improved Code Quality: Clear type definitions and interfaces enhance code readability and maintainability, making it easier for new developers to understand the codebase.
Enhanced Developer Experience: TypeScript provides better tooling and IntelliSense support, speeding up development and reducing the cognitive load on developers.
Scalable Codebase: As the project grows, TypeScript helps manage complexity and ensures consistent data handling across the application.

By integrating TypeScript into their Next.js project, the team enhances development efficiency, reduces bugs, and builds a more maintainable and scalable e-commerce platform.

Advanced Use of TypeScript in Next.js Projects

Leveraging TypeScript in Next.js projects can significantly enhance code quality, maintainability, and developer experience. Here are advanced tips and techniques for using TypeScript in Next.js projects:

Custom App and Document with TypeScript

Customize the default _app.tsx and _document.tsx files to manage the global application state, inject additional HTML, or modify the server-side rendering behavior.

// pages/_app.tsx
import { AppProps } from 'next/app';
import '../styles/globals.css';

function MyApp({ Component, pageProps }: AppProps) {
  return <Component {...pageProps} />;
}

export default MyApp;

// pages/_document.tsx
import Document, { Html, Head, Main, NextScript, DocumentContext } from 'next/document';

class MyDocument extends Document {
  static async getInitialProps(ctx: DocumentContext) {
    const initialProps = await Document.getInitialProps(ctx);
    return { ...initialProps };
  }

  render() {
    return (
      <Html>
        <Head>
          {/* Custom Head Elements */}
        </Head>
        <body>
          <Main />
          <NextScript />
        </body>
      </Html>
    );
  }
}

export default MyDocument;

Advanced Type Safety with Custom Hooks

Create complex custom hooks with generics and conditional types for type-safe state management and data fetching.

import { useState, useEffect } from "react";

interface FetchState<T> {
  data: T | null;
  loading: boolean;
  error: string | null;
}

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

  useEffect(() => {
    const fetchData = async () => {
      try {
        const response = await fetch(url);
        if (!response.ok) {
          throw new Error("Network response was not ok");
        }
        const result: T = await response.json();
        setData(result);
      } catch (error) {
        setError(error.message);
      } finally {
        setLoading(false);
      }
    };
    fetchData();
  }, [url]);

  return { data, loading, error };
}

export default useFetch;

Enhanced Type Declarations and Utility Types

Use advanced TypeScript features like utility types (Partial, Pick, Omit), intersection types, and type guards for more robust type declarations.

interface User {
  id: string;
  name: string;
  email: string;
  role: "admin" | "user";
}

type PartialUser = Partial<User>;
type AdminUser = Omit<User, "role"> & { role: "admin" };

function isAdmin(user: User): user is AdminUser {
  return user.role === "admin";
}

Dynamic Imports with TypeScript

Use dynamic imports for code-splitting and lazy loading components with type safety.

import dynamic from 'next/dynamic';

const DynamicComponent = dynamic(() => import('../components/DynamicComponent'), {
  loading: () => <p>Loading...</p>,
  ssr: false,
});

const Page = () => (
  <div>
    <h1>My Page</h1>
    <DynamicComponent />
  </div>
);

export default Page;

Type-Safe API Routes

Ensure type safety in Next.js API routes by defining request and response types.

import { NextApiRequest, NextApiResponse } from "next";

interface Data {
  message: string;
}

export default function handler(
  req: NextApiRequest,
  res: NextApiResponse<Data>,
) {
  res.status(200).json({ message: "Hello, World!" });
}

Custom Error Handling

Implement custom error handling with TypeScript to improve reliability and user experience.

class CustomError extends Error {
  statusCode: number;

  constructor(message: string, statusCode: number) {
    super(message);
    this.statusCode = statusCode;
    this.name = "CustomError";
  }
}

export function handleError(error: CustomError, res: NextApiResponse) {
  res.status(error.statusCode).json({ message: error.message });
}

Module Augmentation

Extend existing types and modules using TypeScript’s module augmentation feature.

// next-env.d.ts
import "next";
import "next-auth";

declare module "next-auth" {
  interface Session {
    user: {
      id: string;
      role: string;
    };
  }
}

Using TypeScript with Middleware

Create type-safe middleware for custom request handling.

import { NextApiRequest, NextApiResponse } from "next";

export function middleware(
  req: NextApiRequest,
  res: NextApiResponse,
  next: () => void,
) {
  // Custom middleware logic
  next();
}

Optimizing with TypeScript Plugins

Use TypeScript plugins to improve performance and development experience, such as next-plugin-typescript.

// next.config.js
const withTypescript = require("@zeit/next-typescript");
module.exports = withTypescript();

Static Typing for CSS Modules

Ensure type safety for CSS modules by creating type declarations for styles.

declare module "*.module.css" {
  const classes: { [key: string]: string };
  export default classes;
}

Type-Safe Context and State Management

Use TypeScript with context API and state management libraries like Redux for robust type-safe state management.

import { createContext, useContext, useReducer, ReactNode } from 'react';

interface State {
  count: number;
}

const initialState: State = { count: 0 };

type Action = { type: 'increment' } | { type: 'decrement' };

function reducer(state: State, action: Action): State {
  switch (action.type) {
    case 'increment':
      return { count: state.count + 1 };
    case 'decrement':
      return { count: state.count - 1 };
    default:
      throw new Error('Unknown action');
  }
}

const StateContext = createContext<[State, React.Dispatch<Action>]>([initialState, () => {}]);

export function useStateContext() {
  return useContext(StateContext);
}

export function StateProvider({ children }: { children: ReactNode }) {
  const [state, dispatch] = useReducer(reducer, initialState);

  return (
    <StateContext.Provider value={[state, dispatch]}>
      {children}
    </StateContext.Provider>
  );
}

By implementing these advanced TypeScript techniques, you can create more scalable, maintainable, and robust Next.js applications.

NextJs FAQ

To set up a Next.js project with TypeScript, initialize a new project, install TypeScript and required types, and add a tsconfig.json file.

Code:

npx create-next-app my-app --typescript
cd my-app
npm install typescript @types/react @types/node
# Next.js automatically creates tsconfig.json on startup
npm run dev

Add TypeScript to an existing Next.js project by installing TypeScript and necessary types, then creating a tsconfig.json file.

Code:

npm install typescript @types/react @types/node
# Create tsconfig.json file
npx next dev

Benefits include improved code quality through static type checking, better developer experience with IntelliSense, easier refactoring, and reduced runtime errors.

Benefits:

Static Type Checking: Detects type errors during development.
Enhanced IDE Support: Provides better code completion and navigation.
Refactoring: Simplifies refactoring with type safety.
Documentation: Serves as self-documentation for code.

Configure custom paths and aliases in tsconfig.json and next.config.js.

Example:

// tsconfig.json
{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "@components/*": ["components/*"],
      "@lib/*": ["lib/*"]
    }
  }
}

// next.config.js
module.exports = {
  webpack: (config, { isServer }) => {
    config.resolve.alias['@components'] = path.join(__dirname, 'components');
    config.resolve.alias['@lib'] = path.join(__dirname, 'lib');
    return config;
  }
};

Advanced features include using generics, utility types, type guards, and mapped types to create more flexible and robust type definitions.

Examples:

Generics: Create reusable components and functions.

function useData<T>(
  initialValue: T,
): [T, React.Dispatch<React.SetStateAction<T>>] {
  const [data, setData] = useState<T>(initialValue);
  return [data, setData];
}

Utility Types: Simplify complex type transformations.

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

type UserWithoutEmail = Omit<User, "email">;

Conclusion

Integrating TypeScript into your Next.js project provides numerous benefits, from enhanced developer experience to improved code quality and maintainability. With its seamless integration, powerful type system, and early error detection, TypeScript can significantly improve the robustness and scalability of your Next.js applications. By following the setup guide and leveraging TypeScript’s features, you can build more reliable, maintainable, and efficient applications.