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Contributing to Next.js

Watch the 40-minute walkthrough video on how to contribute to Next.js.


Developing

The development branch is canary. This is the branch that all pull requests should be made against. The changes on the canary branch are published to the @canary tag on npm regularly.

To develop locally:

  1. Fork this repository to your own GitHub account and then clone it to your local device.

  2. Create a new branch:

    git checkout -b MY_BRANCH_NAME
    
  3. Install yarn:

    npm install -g yarn
    
  4. Install the dependencies with:

    yarn
    
  5. Start developing and watch for code changes:

    yarn dev
    
  6. In a new terminal, run yarn types to compile declaration files from TypeScript.

    Note: You may need to repeat this step if your types get outdated.

For instructions on how to build a project with your local version of the CLI, see Developing with your local version of Next.js below. (Naively linking the binary is not sufficient to develop locally.)

Building

You can build the project, including all type definitions, with:

yarn build
# - or -
yarn prepublish

By default the latest canary of the next-swc binaries will be installed and used. If you are actively working on Rust code or you need to test out the most recent Rust code that hasn't been published as a canary yet you can install Rust and run yarn --cwd packages/next-swc build-native.

If you need to clean the project for any reason, use yarn clean.

Testing

See the testing readme for information on writing tests.

Running tests

yarn testonly

If you would like to run the tests in headless mode (with the browser windows hidden) you can do

yarn testheadless

Running a specific test suite (e.g. production) inside of the test/integration directory:

yarn testonly --testPathPattern "production"

Running one test in the production test suite:

yarn testonly --testPathPattern "production" -t "should allow etag header support"

Linting

To check the formatting of your code:

yarn lint

If you get errors, you can fix them with:

yarn lint-fix

Running the example apps

Running examples can be done with:

yarn next ./test/integration/basic
# OR
yarn next ./examples/basic-css/

To figure out which pages are available for the given example, you can run:

EXAMPLE=./test/integration/basic
(\
  cd $EXAMPLE/pages; \
  find . -type f \
  | grep -v '\.next' \
  | sed 's#^\.##' \
  | sed 's#index\.js##' \
  | sed 's#\.js$##' \
  | xargs -I{} echo localhost:3000{} \
)

Developing with your local version of Next.js

There are two options to develop with your local version of the codebase:

Set as a local dependency in package.json

  1. In your app's package.json, replace:

    "next": "<next-version>",

    with:

    "next": "file:/path/to/next.js/packages/next",
  2. In your app's root directory, make sure to remove next from node_modules with:

    rm -rf ./node_modules/next
  3. In your app's root directory, run:

    yarn

    to re-install all of the dependencies.

    Note that Next will be copied from the locally compiled version as opposed to from being downloaded from the NPM registry.

  4. Run your application as you normally would.

  5. To update your app's dependencies, after you've made changes to your local next repository. In your app's root directory, run:

    yarn install --force

Troubleshooting

  • If you see the below error while running yarn dev with next:
Failed to load SWC binary, see more info here: https://nextjs.org/docs/messages/failed-loading-swc

Try to add the below section to your package.json, then run again

"optionalDependencies": {
  "@next/swc-linux-x64-gnu": "canary",
  "@next/swc-win32-x64-msvc": "canary",
  "@next/swc-darwin-x64": "canary",
  "@next/swc-darwin-arm64": "canary"
},

Develop inside the monorepo

  1. Move your app inside of the Next.js monorepo.

  2. Run with yarn next-with-deps ./app-path-in-monorepo

This will use the version of next built inside of the Next.js monorepo and the main yarn dev monorepo command can be running to make changes to the local Next.js version at the same time (some changes might require re-running yarn next-with-deps to take effect).

Adding warning/error descriptions

In Next.js we have a system to add helpful links to warnings and errors.

This allows for the logged message to be short while giving a broader description and instructions on how to solve the warning/error.

In general, all warnings and errors added should have these links attached.

Below are the steps to add a new link:

  1. Run yarn new-error which will create the error document and update the manifest automatically.

  2. Add the following url to your warning/error: https://nextjs.org/docs/messages/<file-path-without-dotmd>.

    For example, to link to errors/api-routes-static-export.md you use the url: https://nextjs.org/docs/messages/api-routes-static-export

Adding examples

When you add an example to the examples directory, don’t forget to add a README.md file with the following format:

  • Replace DIRECTORY_NAME with the directory name you’re adding.
  • Fill in Example Name and Description.
  • Examples should be TypeScript first, if possible.
  • You don’t need to add name or version in your package.json.
  • Ensure all your dependencies are up to date.
  • Ensure you’re using next/image.
  • To add additional installation instructions, please add it where appropriate.
  • To add additional notes, add ## Notes section at the end.
  • Remove the Deploy your own section if your example can’t be immediately deployed to Vercel.
# Example Name

Description

## Deploy your own

Deploy the example using [Vercel](https://vercel.com?utm_source=github&utm_medium=readme&utm_campaign=next-example):

[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/new/git/external?repository-url=https://github.com/vercel/next.js/tree/canary/examples/DIRECTORY_NAME&project-name=DIRECTORY_NAME&repository-name=DIRECTORY_NAME)

## How to use

Execute [`create-next-app`](https://github.com/vercel/next.js/tree/canary/packages/create-next-app) with [npm](https://docs.npmjs.com/cli/init) or [Yarn](https://yarnpkg.com/lang/en/docs/cli/create/) to bootstrap the example:

```bash
npx create-next-app --example DIRECTORY_NAME DIRECTORY_NAME-app
# or
yarn create next-app --example DIRECTORY_NAME DIRECTORY_NAME-app
```

Deploy it to the cloud with [Vercel](https://vercel.com/new?utm_source=github&utm_medium=readme&utm_campaign=next-example) ([Documentation](https://nextjs.org/docs/deployment)).

Publishing

Repository maintainers can use yarn publish-canary to publish a new version of all packages to npm.