description:Learn how to transition an existing Create React App project to Next.js.
---
# Migrating from Create React App
This guide will help you understand how to transition from an existing non-ejected Create React App project to Next.js. Migrating to Next.js will allow you to:
- Choose which [data fetching](/docs/basic-features/data-fetching.md) strategy you want on a per-page basis.
- Use [Incremental Static Regeneration](/docs/basic-features/data-fetching.md#incremental-static-regeneration) to update _existing_ pages by re-rendering them in the background as traffic comes in.
- Use [API Routes](/docs/api-routes/introduction.md).
And more! Let’s walk through a series of steps to complete the migration.
## Updating `package.json` and dependencies
The first step towards migrating to Next.js is to update `package.json` and dependencies. You should:
- Remove `react-scripts` (but keep `react` and `react-dom`). If you're using React Router, you can also remove `react-router-dom`.
- Install `next`.
- Add Next.js related commands to `scripts`. One is `next dev`, which runs a development server at `localhost:3000`. You should also add `next build` and `next start` for creating and starting a production build.
Here's an example `package.json`:
```json
{
"scripts":{
"dev":"next dev",
"build":"next build",
"start":"next start"
},
"dependencies":{
"next":"latest",
"react":"latest",
"react-dom":"latest"
}
}
```
## Static Assets and Compiled Output
Create React App uses the `public` directory for the [entry HTML file](https://create-react-app.dev/docs/using-the-public-folder), whereas Next.js uses it for static assets. It's possible to add static assets here, but Create React App recommends importing them directly from JavaScript files.
- Move any images, fonts, or other static assets to `public`.
- Convert `index.html` (the entry point of your application) to Next.js. Any `<head>` code should be moved to a [custom `_document.js`](/docs/advanced-features/custom-document.md). Any shared layout between all pages should be moved to a [custom `_app.js`](/docs/advanced-features/custom-app.md).
- See [Styling](#styling) for CSS/Sass files.
- Add `.next` to `.gitignore`.
## Creating Routes & Linking
With Create React App, you're likely using React Router. Instead of using a third-party library, Next.js includes it's own [file-system based routing](/docs/routing/introduction.md).
- Convert all `Route` components to new files in the `pages` directory.
- For routes that require dynamic content (e.g. `/blog/:slug`), you can use [Dynamic Routes](/docs/routing/dynamic-routes.md) with Next.js (e.g. `pages/blog/[slug].js`). The value of `slug` is accessible through a [query parameter](/docs/routing/dynamic-routes.md). For example, the route `/blog/first-post` would forward the query object `{ 'slug': 'first-post' }` to `pages/blog/[slug].js` ([learn more here](/docs/basic-features/data-fetching.md#getstaticpaths-static-generation)).
For more information, see [Migrating from React Router](/docs/migrating/from-react-router.md).
## Styling
Next.js has built-in support for [CSS](/docs/basic-features/built-in-css-support.md), [Sass](/docs/basic-features/built-in-css-support.md#sass-support) and [CSS-in-JS](/docs/basic-features/built-in-css-support.md#css-in-js).
With Create React App, you can import `.css` files directly inside React components. Next.js allows you to do the same, but requires these files to be [CSS Modules](/docs/basic-features/built-in-css-support.md). For global styles, you'll need a [custom `_app.js`](/docs/advanced-features/custom-app.md) to add a [global stylesheet](docs/basic-features/built-in-css-support.md#adding-a-global-stylesheet).
## Safely Accessing Web APIs
With client-side rendered applications (like Create React App), you can access `window`, `localStorage`, `navigator`, and other [Web APIs](https://developer.mozilla.org/en-US/docs/Web/API) out of the box.
Since Next.js uses [pre-rendering](/docs/basic-features/pages.md#pre-rendering), you'll need to safely access those Web APIs only when you're on the client-side. For example, the following code snippet will allow access to `window` only on the client-side.
```jsx
if(typeofwindow!=='undefined'){
// You now have access to `window`
}
```
A recommended way of accessing Web APIs safely is by using the [`useEffect`](https://reactjs.org/docs/hooks-effect.html) hook, which only executes client-side:
```jsx
import{useEffect}from'react'
useEffect(()=>{
// You now have access to `window`
},[])
```
## Image Component and Image Optimization
Since version **10.0.0**, Next.js has a built-in [Image Component and Automatic Image Optimization](/docs/basic-features/image-optimization.md).
The Next.js Image Component, [`next/image`](/docs/api-reference/next/image.md), is an extension of the HTML `<img>` element, evolved for the modern web.
The Automatic Image Optimization allows for resizing, optimizing, and serving images in modern formats like [WebP](https://developer.mozilla.org/en-US/docs/Web/Media/Formats/Image_types) when the browser supports it. This avoids shipping large images to devices with a smaller viewport. It also allows Next.js to automatically adopt future image formats and serve them to browsers that support those formats.
Instead of optimizing images at build time, Next.js optimizes images on-demand, as users request them. Your build times aren't increased, whether shipping 10 images or 10 million images.
```jsx
importImagefrom'next/image'
exportdefaultfunctionHome(){
return(
<>
<h1>My Homepage</h1>
<Image
src="/me.png"
alt="Picture of the author"
width={500}
height={500}
/>
<p>Welcome to my homepage!</p>
</>
)
}
```
## Environment Variables
Next.js has support for `.env`[Environment Variables](/docs/basic-features/environment-variables.md) similar to Create React App. The main different is the prefix used to expose environment variables on the client-side.
- Change all environment variables with the `REACT_APP_` prefix to `NEXT_PUBLIC_`.
- Server-side environment variables will be available at build-time and in [API Routes](/docs/api-routes/introduction.md).
## Search Engine Optimization
Most Create React App examples use `react-helmet` to assist with adding `meta` tags for proper SEO. With Next.js, we use [`next/head`](/docs/api-reference/next/head.md) to add `meta` tags to your `<head />` element. For example, here's an SEO component with Create React App:
If you want to move your existing Create React App to Next.js and keep a Single-Page App, you can move your old application entry point to an [Optional Catch-All Route](/docs/routing/dynamic-routes.md#optional-catch-all-routes) named `pages/[[…app]].js`.
If you've ejected Create React App, here are some things to consider:
- If you have custom file loaders set up for CSS, Sass, or other assets, this is all built-in with Next.js.
- If you've manually added [new JavaScript features](/docs/basic-features/supported-browsers-features.md#javascript-language-features)(e.g. Optional Chaining) or [Polyfills](/docs/basic-features/supported-browsers-features.md#polyfills), check to see what's included by default with Next.js.
- If you have a custom code splitting setup, you can remove that. Next.js has automatic code splitting on a [per-page basis](/docs/basic-features/pages.md).
- You can [customize your PostCSS setup](/docs/advanced-features/customizing-postcss-config.md#default-behavior) with Next.js without ejecting from the framework.
- You should reference the default [Babel config](/docs/advanced-features/customizing-babel-config.md) and [Webpack config](/docs/api-reference/next.config.js/custom-webpack-config.md) of Next.js to see what's included by default.
## Learn More
You can learn more about Next.js by completing our [starter tutorial](https://nextjs.org/learn/basics/getting-started). If you have questions or if this guide didn't work for you, feel free to reach out to our community on [GitHub Discussions](https://github.com/vercel/next.js/discussions).
