TypeScript

Next.js provides a TypeScript-first development experience for building your React application.

It comes with built-in TypeScript support for automatically installing the necessary packages and configuring the proper settings.

New Projects

create-next-app now ships with TypeScript by default.

npx create-next-app@latest

Existing Projects

Add TypeScript to your project by renaming a file to .ts / .tsx. Run next dev and next build to automatically install the necessary dependencies and add a tsconfig.json file with the recommended config options.

If you already had a jsconfig.json file, copy the paths compiler option from the old jsconfig.json into the new tsconfig.json file, and delete the old jsconfig.json file.

We also recommend you to use next.config.ts over next.config.js for better type inference.

Minimum TypeScript Version

It is highly recommended to be on at least v4.5.2 of TypeScript to get syntax features such as type modifiers on import names and performance improvements.

Type checking in Next.js Configuration

Type checking next.config.js

When using the next.config.js file, you can add some type checking in your IDE using JSDoc as below:

// @ts-check
 
/** @type {import('next').NextConfig} */
const nextConfig = {
  /* config options here */
}
 
module.exports = nextConfig

Type checking next.config.ts

You can use TypeScript and import types in your Next.js configuration by using next.config.ts.

import type { NextConfig } from 'next'
 
const nextConfig: NextConfig = {
  /* config options here */
}
 
export default nextConfig

Good to know: You can import Native ESM modules in next.config.ts without any additional configuration. Supports importing extensions like .cjs, .cts, .mjs, and .mts.

Static Generation and Server-side Rendering

For getStaticProps, getStaticPaths, and getServerSideProps, you can use the GetStaticProps, GetStaticPaths, and GetServerSideProps types respectively:

import type { GetStaticProps, GetStaticPaths, GetServerSideProps } from 'next'
 
export const getStaticProps = (async (context) => {
  // ...
}) satisfies GetStaticProps
 
export const getStaticPaths = (async () => {
  // ...
}) satisfies GetStaticPaths
 
export const getServerSideProps = (async (context) => {
  // ...
}) satisfies GetServerSideProps

Good to know: satisfies was added to TypeScript in 4.9. We recommend upgrading to the latest version of TypeScript.

API Routes

The following is an example of how to use the built-in types for API routes:

import type { NextApiRequest, NextApiResponse } from 'next'
 
export default function handler(req: NextApiRequest, res: NextApiResponse) {
  res.status(200).json({ name: 'John Doe' })
}

You can also type the response data:

import type { NextApiRequest, NextApiResponse } from 'next'
 
type Data = {
  name: string
}
 
export default function handler(
  req: NextApiRequest,
  res: NextApiResponse<Data>
) {
  res.status(200).json({ name: 'John Doe' })
}

Custom App

If you have a custom App, you can use the built-in type AppProps and change file name to ./pages/_app.tsx like so:

import type { AppProps } from 'next/app'
 
export default function MyApp({ Component, pageProps }: AppProps) {
  return <Component {...pageProps} />
}

Path aliases and baseUrl

Next.js automatically supports the tsconfig.json "paths" and "baseUrl" options.

You can learn more about this feature on the Module Path aliases documentation.

Incremental type checking

Since v10.2.1 Next.js supports incremental type checking when enabled in your tsconfig.json, this can help speed up type checking in larger applications.

Ignoring TypeScript Errors

Next.js fails your production build (next build) when TypeScript errors are present in your project.

If you'd like Next.js to dangerously produce production code even when your application has errors, you can disable the built-in type checking step.

If disabled, be sure you are running type checks as part of your build or deploy process, otherwise this can be very dangerous.

Open next.config.ts and enable the ignoreBuildErrors option in the typescript config:

import type { NextConfig } from 'next'
 
const nextConfig: NextConfig = {
  typescript: {
    // !! WARN !!
    // Dangerously allow production builds to successfully complete even if
    // your project has type errors.
    // !! WARN !!
    ignoreBuildErrors: true,
  },
}
 
export default nextConfig

Good to know: You can run tsc --noEmit to check for TypeScript errors yourself before building. This is useful for CI/CD pipelines where you'd like to check for TypeScript errors before deploying.

Custom Type Declarations

When you need to declare custom types, you might be tempted to modify next-env.d.ts. However, this file is automatically generated, so any changes you make will be overwritten. Instead, you should create a new file, let's call it new-types.d.ts, and reference it in your tsconfig.json:

{
  "compilerOptions": {
    "skipLibCheck": true
    //...truncated...
  },
  "include": [
    "new-types.d.ts",
    "next-env.d.ts",
    ".next/types/**/*.ts",
    "**/*.ts",
    "**/*.tsx"
  ],
  "exclude": ["node_modules"]
}

Version Changes