TypeScript

Version History
VersionChanges
v12.0.0SWC is now used by default to compile TypeScript and TSX for faster builds.
v10.2.1Incremental type checking support added when enabled in your tsconfig.json.

Next.js provides an integrated TypeScript experience, including zero-configuration set up and built-in types for Pages, APIs, and more.

create-next-app support

You can create a TypeScript project with create-next-app using the --ts, --typescript flag like so:

npx create-next-app@latest --ts
# or
yarn create next-app --typescript
# or
pnpm create next-app --ts

Existing projects

To get started in an existing project, create an empty tsconfig.json file in the root folder:

touch tsconfig.json

Next.js will automatically configure this file with default values. Providing your own tsconfig.json with custom compiler options is also supported.

You can also provide a relative path to a tsconfig.json file by setting typescript.tsconfigPath prop inside your next.config.js file.

Starting in v12.0.0, Next.js uses SWC by default to compile TypeScript and TSX for faster builds.

Next.js will use Babel to handle TypeScript if .babelrc is present. This has some caveats and some compiler options are handled differently.

Then, run next (normally npm run dev or yarn dev) and Next.js will guide you through the installation of the required packages to finish the setup:

npm run dev

# You'll see instructions like these:
#
# Please install TypeScript, @types/react, and @types/node by running:
#
#         yarn add --dev typescript @types/react @types/node
#
# ...

You're now ready to start converting files from .js to .tsx and leveraging the benefits of TypeScript!

A file named next-env.d.ts will be created in the root of your project. This file ensures Next.js types are picked up by the TypeScript compiler. You cannot remove it or edit it as it can change at any time. As such this file should not be committed and should be ignored by version control.

TypeScript strict mode is turned off by default. When you feel comfortable with TypeScript, it's recommended to turn it on in your tsconfig.json.

Instead of editing next-env.d.ts, you can include additional types by adding a new file e.g. additional.d.ts and then referencing it in the include array in your tsconfig.json.

By default, Next.js will do type checking as part of next build. We recommend using code editor type checking during development.

If you want to silence the error reports, refer to the documentation for Ignoring TypeScript errors.

Static Generation and Server-side Rendering

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

import { GetStaticProps, GetStaticPaths, GetServerSideProps } from 'next'

export const getStaticProps: GetStaticProps = async (context) => {
  // ...
}

export const getStaticPaths: GetStaticPaths = async () => {
  // ...
}

export const getServerSideProps: GetServerSideProps = async (context) => {
  // ...
}

If you're using getInitialProps, you can follow the directions on this page.

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 (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 (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.

Type checking next.config.js

The next.config.js file must be a JavaScript file as it does not get parsed by Babel or TypeScript, however 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

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.

It is highly recommended to be on at least v4.3.2 of TypeScript to experience the best performance when leveraging this feature.

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.js and enable the ignoreBuildErrors option in the typescript config:

module.exports = {
  typescript: {
    // !! WARN !!
    // Dangerously allow production builds to successfully complete even if
    // your project has type errors.
    // !! WARN !!
    ignoreBuildErrors: true,
  },
}