Next js typescript install

A Guide for Next.js with TypeScript

Next.js is an open source React framework for building single-page web applications. It comes with numerous out-of-the-box functionalities that make developing web applications faster and more interesting, thereby providing refined and elegant developer and user experiences.

Combining Next.js and TypeScript gives us superpowers to rapidly create applications with a good developer and user experiences. Every developer hates bugs. Especially pesky ones such as typos or trying to use or access undeclared variables. TypeScript helps catch these types of bugs early during development, and this is one of the many features that make integrating it with a tool like Next.js fantastic.

In this article, we’ll look at how you can integrate TypeScript in your Next.js apps. We’ll also explore reasons why you should consider using this tool in your Next.js projects and also talk about its benefits.

What is TypeScript?​

It’s a strict JavaScript superset used for large enterprise projects and writing programs that scale. In the end, TypeScript transpiles to plain JavaScript and can be used for developing applications on the client-side and server-side.

TypeScript is an object-oriented programming language that provides all JavaScript features and extra useful capabilities. These capabilities include static or dynamic type checking, error checking during compilation, type inference, and so on.

How to add TypeScript to your Next.js app​

Next.js provides integrated support for TypeScript with built-in types for pages, API routes, the three data fetching methods, etc.

Basically, there are two ways in which we can add TypeScript to our project. The first is with create-next-app , and the second is by adding TypeSript manually to an existing project.

create-next-app ​

We can bootstrap a Next.js application with TypeScript by adding a —typescript or —ts flag to the create-next-app command like below:

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

Adding TypeScript to an existing project​

Alternatively, we can also add TypeScript manually to an existing Next.js project.

First, you’ll need to create a tsconfig.json file in your project root folder. This file specifies the root files and the compiler options required to compile the project and is populated automatically by Next.js with default values.

Next, run npm run dev or yarn dev (if you use Yarn) to start the application development server.

Next.js will emit a message in the terminal with the following content and try to install the necessary TypeScript related packages:

It looks like you're trying to use TypeScript but do not have the required package(s) installed. Installing dependencies If you are not trying to use TypeScript, please remove the tsconfig.json file from your package root (and any TypeScript files in your pages directory).  Installing devDependencies (yarn): - typescript - @types/react - @types/node [1/4] Resolving packages. [2/4] Fetching packages. 

When the installation is complete, open tsconfig.json and you’ll see it populated with values like below:

If you noticed, Next.js also created a new file, next-env.d.ts in the project root. This file ensures Next.js types are picked up by the compiler and should not be edited or deleted. Also, ensure the file is added to .gitignore to prevent it from being committed by version control like Git.

With this, you can now start creating files with .ts and .tsx extensions in your application.

Usage example

import React from 'react'  type ProfileProps =   profile:   firstName: string,  lastName: string,  age: number, > >  const Profile: React.FunctionComponentProfileProps> = ( profile >): JSX.Element =>   return ( > p>Profilep> div>Welcome, profile.firstName>div> > ) >  export default Profile; 

How to use Typescript with Next.js data fetching methods​

Next.js comes with built-in types for all its three data fetching methods ( getStaticProps , getServerSideProps , and getStaticPaths ).

Here’s how to use them in your code:

import  GetStaticProps, GetStaticPaths, GetServerSideProps > from 'next'  export const getStaticProps: GetStaticProps = async (context) => >  export const getStaticPaths: GetStaticPaths = async () => >  export const getServerSideProps: GetServerSideProps = async (context) => > 

Next.js also provides built-in types to infer the types for props from getServerSideProps and getStaticProps .

If you want to get inferred typings for your props, you can use InferGetStaticPropsType or InferGetServerSidePropsType in a page component.

Let’s say we’re expecting some data from an API that we need to pre-render at build time. Instead of writing repetitive code like the below:

type PostProps=   userId: number,  id: number,  title: string,  body: string >  export const getStaticProps = async () =>   const response = await fetch('https://jsonplaceholder.typicode.com/posts'); const posts: PostProps[] = await response.json();  return   props:   posts, >, > >  function PostPage( posts >:  posts: PostProps >)   . >  export default PostPage; 

We can use InferGetStaticPropsType to get inferred typings for the posts prop. Add and refactor the code with the highlighted like below:

import  InferGetStaticPropsType > from 'next'  .  function PostPage( posts >: InferGetStaticPropsTypetypeof getStaticProps>) >  export default PostPage 

You can also use this same method when using getServerSideProps .

How to use Typescript in Next.js API routes​

Next.js also comes with built-in types for API routes. which we can access like below:

import type  NextApiRequest, NextApiResponse > from 'next'  export default (req: NextApiRequest, res: NextApiResponse) =>   res.status(200).json( age: '25' >) > 

We can also specify custom types for the response data:

import type  NextApiRequest, NextApiResponse > from 'next'  type Data =   name: string >  export default (req: NextApiRequest, res: NextApiResponseData>) =>   res.status(200).json( age: '25' >) > 

How to configure absolute imports and module path aliases in tsconfig.json​

Do you relate with the pain of having to do something like this?

Import  fetchUserProfile > from '../../../../utils' Import UserProfile from '../../../UserProfile' 

How about if you could do something like?

Import  fetchUserProfile > from '/@utils' Import UserProfile from '@components/UserProfile' 

Well, to achieve this, we can configure path aliases in tsconfig.json so we can conveniently import modules across our application. TypeScript path aliases allow us to create aliases or shortcuts for absolute paths in the application, which we can resolve to. Next.js also automatically supports path aliases, so we don’t have to do many configurations.

For example, if you have a file in your project importing a module with a path structure like /components/MUIComponents/ButtonGroup/ , instead of trying to write an ugly code such as this:

import React from "react"; import ButtonGroup from import ButtonGroup from "../../components/MUIComponents/ButtonGroup";  const User = () =>   return ( > h1>User Pageh1> div> ButtonGroup /> div> > ); >;  export default User; 

We can create a path alias for all files in the MUIComponents folder for easy access using the baseUrl and path options in tsconfig.json like so:

. "baseUrl": ".", "paths":   "@/MUIComponents/*": ["components/MUIComponents/*"] >, . 

baseUrl lets us specify a root URL to use for our imports and paths lets us configure path aliases. You can read more about module path aliases here.

You can use a jsconfig.json file instead if you’re not using TypeScript in your project.

Now we can use the alias in our application like so:

import ButtonGroup from "@/MUIComponents/ButtonGroup";  const User = () =>   return ( > h1>User Pageh1> div> ButtonGroup /> div> > ); >;  export default User; 

This looks way better and straightforward.

Disabling Typescript Errors in Production​

If you happen to have TypeScript errors while running next build , Next.js will fail the build but you can disable the type checks if you wish.

To disable the type checking step, enable the ignoreBuildErrors option in next.config.js like so:

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

Make sure you really know what you’re doing before using this option.

Conclusion​

We covered how to get started with TypeScript in your Next.js applications. We also talked about the importance and benefits associated with combining TypeScript capabilities with Next.js for a faster and easier application development experience. We hope this article helps you consider integrating TypeScript and Next.js in your next applications.

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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.

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.

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

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) =>  // .  >

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: NextApiResponseData> )  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 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  **/ const nextConfig =  /* config options here */ > module.exports = nextConfig

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.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,  >, >

Version Changes

Version	Changes
v13.2.0	Statically typed links are available in beta.
v12.0.0	SWC is now used by default to compile TypeScript and TSX for faster builds.
v10.2.1	Incremental type checking

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