# Contributing to Next.js

Read about our [Commitment to Open Source](https://vercel.com/oss). To
contribute to [our examples](examples), please see **[Adding
examples](#adding-examples)** below.

## Developing

The development branch is `canary`, and this is the branch that all pull
requests should be made against. After publishing a stable release, the changes
in the `canary` branch are rebased into `master`. The changes on the `canary`
branch are published to the `@canary` dist-tag daily.

To develop locally:

1. [Fork](https://help.github.com/articles/fork-a-repo/) this repository to your
   own GitHub account and then
   [clone](https://help.github.com/articles/cloning-a-repository/) 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   _Note: You may need to repeat this step if your types get outdated._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](#developing-with-your-local-version-of-nextjs)**
below. (Naively linking the binary is not sufficient to develop locally.)

## Building

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

```bash
yarn build
# - or -
yarn prepublish
```

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

## Testing

Make sure you have `chromedriver` installed, and it should match your Chrome version.
You can install it with:

- `apt install chromedriver` on Ubuntu/Debian
- `brew install --cask chromedriver` on Mac OS X
- `chocolatey install chromedriver` on Windows

- Or manually download the version that matches your installed chrome version (if there's no match, download a version under it, but not above) from the [chromedriver repo](https://chromedriver.storage.googleapis.com/index.html) and add the binary to `<next-repo>/node_modules/.bin`

You may also have to [install Rust](https://www.rust-lang.org/tools/install) and build our native packages to see all tests pass locally. We check in binaries for the most common targets and those required for CI so that most people don't have to, but if you do not see a binary for your target in `packages/next/native`, you can build it by running `yarn --cwd packages/next build-native`. If you are working on the Rust code and you need to build the binaries for ci, you can manually trigger [the workflow](https://github.com/vercel/next.js/actions/workflows/build_native.yml) to build and commit with the "Run workflow" button.

### Running tests

```sh
yarn testonly
```

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

```sh
yarn testheadless
```

If you would like to use a specific Chrome/Chromium binary to run tests you can specify it with

```sh
CHROME_BIN='path/to/chrome/bin' yarn testonly
```

Running a specific test suite inside of the `test/integration` directory:

```sh
yarn testonly --testPathPattern "production"
```

Running one test in the `production` test suite:

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

### Running the integration apps

Running examples can be done with:

```sh
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:

```sh
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 local dependency in package.json

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

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

   with:

   ```json
   "next": "file:/path/to/next.js/packages/next",
   ```

2. In your app's root directory, make sure to remove `next` from `node_modules` with:

   ```sh
   rm -rf ./node_modules/next
   ```

3. In your app's root directory, run:

   ```sh
   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:

   ```sh
   yarn install --force
   ```

or

### 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 affect).

## 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. Create a new markdown file under the `errors` directory based on
   `errors/template.md`:

   ```shell
   cp errors/template.md errors/<error-file-name>.md
   ```

2. Add the newly added file to `errors/manifest.json`
3. 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](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`.
- 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.
- Remove the `Preview` section if the example doesn't work on [StackBlitz](http://stackblitz.com/) and file an issue [here](https://github.com/stackblitz/webcontainer-core).

````markdown
# Example Name

Description

## Preview

Preview the example live on [StackBlitz](http://stackblitz.com/):

[![Open in StackBlitz](https://developer.stackblitz.com/img/open_in_stackblitz.svg)](https://stackblitz.com/github/vercel/next.js/tree/canary/examples/DIRECTORY_NAME)

## 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.