NextJs Monorepo

Monorepo concepts, tips and tricks oriented around NextJs

Howtos for monorepo. New to monorepos ? check this FAQ. This example is managed by Yarn 3.1+ / typescript path aliases and tries to be as strict and standard as possible.

Useful to

• Establish a structure and demonstrate a lifecycle perspective (dx, ci/cd, deployments...)
• How to create and consume shared packages, locales, assets, api types...
• Integrate tools & configs (eslint, jest, changelogs, versioning, codecov, codeclimate...).
• Clarify some advantages of monorepos (team cohesion, consistency, duplication, refactorings, atomic commits...).
• Create nextjs/vercel/prisma... bug reports with reproducible examples (initial goal of this repo).

Structure

.
├── apps
│   ├── blog-app
│   ├── vite-app
│   └── web-app
└── packages
    ├── core-lib
    ├── db-main-prisma
    └── ui-lib

Example apps

• apps/web-app: SSR, i18n, GraphQL, Rest. README | DEMO/Vercel | CHANGELOG
• apps/blog-app: SSG. README | DEMO/Vercel | CHANGELOG
• apps/vite-app: Basic vite-app. README | DEMO/Vercel | CHANGELOG

Apps should not depend on apps, they can depend on packages

Example shared packages

• packages/core-lib: used by web-app and blog-app, publishable. README | CHANGELOG
• packages/db-main-prisma: used by web-app. README | CHANGELOG
• packages/ui-lib: used by web-app and blog-app, publishable. README | CHANGELOG

Apps can depend on packages, packages can depend on each others...

Shared static assets

If needed static resources like locales, images,... can be shared by using symlinks in the repo.

• See the global static folder.

Folder overview

Detailed folder structure

.
├── apps
│   ├── blog-app                 (NextJS SSG app)
│   │   ├── public/
│   │   │   └── shared-assets/   (symlink to global static/assets)
│   │   ├── src/
│   │   ├── CHANGELOG.md         (autogenerated with changesets)
│   │   ├── jest.config.js
│   │   ├── next.config.js
│   │   ├── package.json         (define package workspace:package deps)
│   │   └── tsconfig.json        (define path to packages)
│   │
│   ├── vite-app                 (Vite app as an example)
│   │   ├── src/
│   │   ├── package.json         (define package workspace:package deps)
│   │   └── tsconfig.json        (define path to packages)
│   │
│   └── web-app                  (NextJS app with api-routes)
│       ├── public/
│       │   ├── shared-assets/   (possible symlink to global assets)
│       │   └── shared-locales/  (possible symlink to global locales)
│       ├── src/
│       │   └── pages/api        (api routes)
│       ├── CHANGELOG.md
│       ├── jest.config.js
│       ├── next.config.js
│       ├── package.json         (define package workspace:package deps)
│       └── tsconfig.json        (define path to packages)
│
├── packages
│   ├── core-lib                 (basic ts libs)
│   │   ├── src/
│   │   ├── CHANGELOG.md
│   │   ├── package.json
│   │   └── tsconfig.json
│   │
│   ├── db-main-prisma          (basic db layer with prisma)
│   │   ├── prisma/
│   │   ├── src/
│   │   ├── CHANGELOG.md
│   │   ├── package.json
│   │   └── tsconfig.json
│   │
│   └── ui-lib                  (basic design-system in react)
│       ├── src/
│       ├── CHANGELOG.md
│       ├── package.json
│       └── tsconfig.json
│
├── static                       (no code: images, json, locales,...)
│   ├── assets
│   └── locales
├── .yarnrc.yml
├── docker-compose.yml           (database service for now)
├── package.json                 (the workspace config)
└── tsconfig.base.json           (base typescript config)

Howto

1. Enable workspace support

Root package.json with workspace directories

{
  "name": "nextjs-monorepo-example",
  // Set the directories where your apps, packages will be placed
  "workspaces": ["apps/*", "packages/*"],
  //...
}

The package manager will scan those directories and look for children package.json. Their content is used to define the workspace topology (apps, libs, dependencies...).

2. Create a new package

Create a folder in ./packages/ directory with the name of your package.

Create the package folder

mkdir packages/magnificent-poney
mkdir packages/magnificent-poney/src
cd packages/magnificent-poney

Initialize a package.json with the name of your package.

Rather than typing yarn init, prefer to take the ./packages/ui-lib/package.json as a working example and edit its values.

Example of package.json

{
  "name": "@your-org/magnificent-poney",
  "version": "0.0.0",
  "private": true,
  "scripts": {
    "clean": "rimraf --no-glob ./tsconfig.tsbuildinfo",
    "lint": "eslint . --ext .ts,.tsx,.js,.jsx",
    "typecheck": "tsc --project ./tsconfig.json --noEmit",
    "test": "run-s 'test:*'",
    "test:unit": "echo \"No tests yet\"",
    "fix:staged-files": "lint-staged --allow-empty",
    "fix:all-files": "eslint . --ext .ts,.tsx,.js,.jsx --fix",
  },
  "devDependencies": {
    "@testing-library/jest-dom": "5.14.1",
    "@testing-library/react": "12.0.0",
    "@testing-library/react-hooks": "7.0.1",
    "@types/node": "16.4.10",
    "@types/react": "17.0.15",
    "@types/react-dom": "17.0.9",
    "@typescript-eslint/eslint-plugin": "4.29.0",
    "@typescript-eslint/parser": "4.29.0",
    "camelcase": "6.2.0",
    "eslint": "7.32.0",
    "eslint-config-prettier": "8.3.0",
    "eslint-plugin-import": "2.23.4",
    "eslint-plugin-jest": "24.4.0",
    "eslint-plugin-jest-formatting": "3.0.0",
    "eslint-plugin-jsx-a11y": "6.4.1",
    "eslint-plugin-prettier": "3.4.0",
    "eslint-plugin-react": "7.24.0",
    "eslint-plugin-react-hooks": "4.2.0",
    "eslint-plugin-testing-library": "4.10.1",
    "jest": "27.0.6",
    "npm-run-all": "4.1.5",
    "prettier": "2.3.2",
    "react": "17.0.2",
    "react-dom": "17.0.2",
    "rimraf": "3.0.2",
    "shell-quote": "1.7.2",
    "ts-jest": "27.0.4",
    "typescript": "4.3.5",
  },
  "peerDependencies": {
    "react": "^16.14.0 || ^17.0.2",
    "react-dom": "^16.14.0 || ^17.0.2",
  },
}

Note that as we want to be strict with dependencies, the best is to define all you need (eslint, ...) per package. And not in the monorepo root. That might seem weird, but on the long run it's much safer.

3. Using the package in app

Step 3.1: package.json

First add the package to the app package.json. The recommended way is to use the workspace protocol supported by yarn and pnpm.

cd apps/my-app
yarn add @your-org/magnificent-poney@'workspace:*'

Inspiration can be found in apps/web-app/package.json.

package.json

{
  "name": "my-app",
  "dependencies": {
    "@your-org/magnificient-poney": "workspace:*",
  },
}

Step 3.2: In tsconfig.json

Then add a typescript path alias in the app tsconfig.json. This will allow you to import it directly (no build needed)

Inspiration can be found in apps/web-app/tsconfig.json.

Example of tsonfig.json

{
  "compilerOptions": {
    "baseUrl": "./src",
    "paths": {
      // regular app aliases
      "@/components/*": ["./components/*"],
      // packages aliases, relative to app_directory/baseUrl
      "@your-org/magnificent-poney/*": [
        "../../../packages/magnificent-poney/src/*",
      ],
      "@your-org/magnificent-poney": [
        "../../../packages/magnificent-poney/src/index",
      ],
    },
  },
}

PS:

• Don't try to set aliases in the global tsonfig.base.json to keep strict with graph dependencies.
• The star in @your-org/magnificent-poney/* allows you to import subfolders. If you use a barrel file (index.ts), the alias with star can be removed.

Step 3.3: Next config

Edit your next.config.js and enable the experimental.externalDir option. Feedbacks here.

const nextConfig = {
  experimental: {
    externalDir: true,
  },
};
export default nextConfig;

Using a NextJs version prior to 10.2.0 ?

If you're using an older NextJs version and don't have the experimental flag, you can simply override your webpack config.

const nextConfig = {
  webpack: (config, { defaultLoaders }) => {
    // Will allow transpilation of shared packages through tsonfig paths
    // @link https://github.com/vercel/next.js/pull/13542
    const resolvedBaseUrl = path.resolve(config.context, "../../");
    config.module.rules = [
      ...config.module.rules,
      {
        test: /\.(tsx|ts|js|jsx|json)$/,
        include: [resolvedBaseUrl],
        use: defaultLoaders.babel,
        exclude: (excludePath) => {
          return /node_modules/.test(excludePath);
        },
      },
    ];
    return config;
  },
};

PS: If your shared package make use of scss bundler... A custom webpack configuration will be necessary or use next-transpile-modules, see FAQ below.

Step 3.4: Using the package

The packages are now linked to your app, just import them like regular packages: import { poney } from '@your-org/magnificent-poney'.

4. Publishing

Optional

If you need to share some packages outside of the monorepo, you can publish them to npm or private repositories. An example based on microbundle is present in each package. Versioning and publishing can be done with atlassian/changeset, and it's simple as typing:

$ yarn changeset

Follow the instructions... and commit the changeset file. A "Version Packages" P/R will appear after CI checks. When merging it, a github action will publish the packages with resulting semver version and generate CHANGELOGS for you.

PS:

• Even if you don't need to publish, changeset can maintain an automated changelog for your apps. Nice !
• To disable automatic publishing of some packages, just set "private": "true" in their package.json.
• Want to tune the behaviour, see .changeset/config.json.

4. Monorepo essentials

Monorepo scripts

Some convenience global scripts are defined in the root package.json, they generally call their counterparts defined in packages and apps.

{
  "scripts": {
    "clean": "yarn workspaces foreach -ptv run clean",
    "test": "run-s 'test:*'",
    "test:unit": "yarn workspaces foreach -ptv run test:unit",
    "fix:staged-files": "yarn workspaces foreach -t run fix:staged-files",
    "fix:all-files": "yarn workspaces foreach -ptv run fix:all-files",
    // Manage versions and releases with atlassion/changesets
    "changeset": "changeset",
    "release": "yarn build && changeset publish",
    // Utility scripts to check/upgrade deps across the entire monorepo
    // use yarn dedupe after install
    "deps:check": "npm-check-updates --deep --dep prod,dev,optional",
    "deps:update": "npm-check-updates -u --deep --dep prod,dev,optional",
    "typecheck": "yarn workspaces foreach -ptv run typecheck",
    "lint": "yarn workspaces foreach -ptv run lint",
    "share:static:symlink": "yarn workspaces foreach -pv --include '*-app' run share:static:symlink",
    "share:static:hardlink": "yarn workspaces foreach -pv --include '*-app' run share:static:hardlink",
    "apps:build": "yarn workspaces foreach -ptv --include '*-app' run build",
    "apps:clean": "yarn workspaces foreach -ptv --include '*-app' run clean",
    "packages:build": "yarn workspaces foreach -ptv --include '@your-org/*' run build",
    "packages:lint": "yarn workspaces foreach -ptv --include '@your-org/*' run lint",
    "packages:typecheck": "yarn workspaces foreach -ptv --include '@your-org/*' run typecheck",
    "packages:clean": "yarn workspaces foreach -ptv --include '@your-org/*' run clean",
    "docker:up": "docker-compose up -d",
    "docker:up:main-db": "docker-compose up -d main-db",
    "docker:down": "docker-compose down",
    "docker:clean": "docker container rm -f $(docker container ls -qa) && docker image rm -f $(docker image ls -q)",
  },
}

PS:

• Convention: whatever the script name (ie: test:unit), keeps it consistent over root commands, packages and apps.
• The use of yarn workspaces commands can be replicated in pnpm, nmp7+lerna...

Maintaining deps updated

The global commands yarn deps:check and yarn deps:update will help to maintain the same versions across the entire monorepo. They are based on the excellent npm-check-updates (see options, i.e: yarn check:deps -t minor).

After running yarn deps:update, a yarn install is required. To prevent having duplicates in the yarn.lock, you can run yarn dedupe --check and yarn dedupe to apply deduplication. The duplicate check is enforced in the example github actions.

5. Quality

5.1 Linters

An example of base eslint configuration can be found in ./.eslint.base.js, apps and packages extends it in their own root folder, as an example see ./apps/web-app/.eslintrc.js. Prettier is included in eslint configuration as well as eslint-config-next for nextjs apps.

For code complexity and deeper code analysis sonarjs plugin is activated.

5.2 Hooks / Lint-staged

Check the .husky folder content to see what hooks are enabled. Lint-staged is used to guarantee that lint and prettier are applied automatically on commit and/or pushes.

5.3 Tests

Tests relies on ts-jest with support for typescript path aliases. React-testing-library is enabled whenever react is involved. Configuration lives in the root folder of each apps/packages. As an example see ./apps/web-app/jest.config.js.

5.4 CI

You'll find some example workflows for github action in .github/workflows. By default, they will ensure that

• You don't have package duplicates.
• You don't have typecheck errors.
• You don't have linter / code-style errors.
• Your test suite is successful.
• Your apps (nextjs) or packages can be successfully built.
• Basic size-limit example in web-app.

Each of those steps can be opted-out.

To ensure decent performance, those features are present in the example actions:

• Caching of packages (node_modules...) - install around 25s

• Caching of nextjs previous build - built around 20s

• Triggered when changed using actions paths, ie:

   paths:
     - "apps/blog-app/**"
     - "packages/**"
     - "package.json"
     - "tsconfig.base.json"
     - "yarn.lock"
     - ".yarnrc.yml"
     - ".github/workflows/**"
     - ".eslintrc.base.json"
     - ".eslintignore"
  

6. Editor support

6.1 VSCode

The ESLint plugin requires that the eslint.workingDirectories setting is set:

"eslint.workingDirectories": [
    {
        "pattern": "./apps/*/"
    },
    {
        "pattern": "./packages/*/"
    }
],

More info here

7. Deploy

Vercel

Vercel support natively monorepos, see the vercel-monorepo-deploy document.

Others

Netlify, aws-amplify, k8s-docker, serverless-nextjs recipes might be added in the future. PR's welcome too.

FAQ

Monorepo

Benefits

• Ease of code reuse. You can easily extract shared libraries (like api, shared ui, locales, images...) and use them across apps without the need of handling them in separate git repos (removing the need to publish, version, test separately...). This limit the tendency to create code duplication amongst developers when time is short.
• Atomic commits. When projects that work together are contained in separate repositories, releases need to sync which versions of one project work with the other. In monorepo CI, sandboxes and releases are much easier to reason about (ie: dependency hell...). A pull-request contains all changes at once, no need to coordinate multiple packages versions to test it integrally (multiple published canary versions...).
• Code refactoring. Changes made on a library will immediately propagate to all consuming apps / packages. Typescript / typechecks, tests, ci, sandboxes... will improve the confidence to make a change (or the right one thanks to improved discoverability of possible side effects). It also limits the tendency to create tech debt as it invites the dev to refactor all the code that depends on a change.
• Collaboration across teams. Consistency, linters, discoverability, duplication... helps to maintain cohesion and collaboration across teams.

Drawbacks

• Increased build time. Generally a concern but not relevant in this context thanks to the combination of nextjs/webpack5, typescript path aliases and yarn. Deps does not need to be build... modified files are included as needed and properly cached (nextjs webpack5, ci, deploy, docker/buildkit...).
• Versioning and publishing. Sometimes a concern when you want to use the shared libraries outside of the monorepo. See the notes about atlassian changeset. Not relevant here.
• Git repo size. All packages and apps and history will fit in the same git repository increasing its size and checkout time. Generally when you reach size problems, check for assets like images first and extract packages that don't churn anymore.
• Multi-languages. Setting up a monorepo containing code in multiple languages (php, ruby, java, node) is extremely difficult to handle due to nonexistence of mature tooling (bazel...).The general idea is to create a monorepo with the same stack (node, typescript...) and managed by the same package manager (yarn, pnpm,...)

Exact vs semver dependencies

Apps dependencies and devDependencies are pinned to exact versions. Packages deps will use semver compatible ones. For more info about this change see reasoning here and our renovabot.json5 configuration file.

To help keeping deps up-to-date, see the yarn deps:check && yarn deps:update scripts and / or use the renovatebot.

When adding a dep through yarn cli (i.e.: yarn add something), it's possible to set the save-exact behaviour automatically by setting defaultSemverRangePrefix: "" in yarnrc.yml. But this would make the default for packages/* as well. Better to handle yarn add something --exact on per-case basis.

About next-transpile-modules

And why this repo example doesn't use it to support package sharing.

next-transpile-modules is one of the most installed packages for nextjs. It basically allows you to transpile some 3rd party packages present in your node_modules folder. This can be helpful for transpiling packages for legacy browser support (ie11), esm packages (till it lands in nextjs) and handle shared packages.

In this repo, we use next-transpile-modules only for ie11 and esm. The monorepo management is done through tsconfig path. It will work best when external tooling is involved (ts-jest...), but comes with some limitations if your shared package use an scss compiler for example. Note that future version of NextJs might improve monorepo support through experimental.externalDir option.

See here a quick comparison:

Support matrix	tsconfig paths	next-transpile-module
Typescript	✅	✅
Javascript	✅	✅
NextJs Fast refresh	✅	✅
CSS	custom webpack cfg	✅
SCSS	custom webpack cfg	✅
CSS-in-JS	✅	✅
ts-jest	✅	custom aliases
Vercel monorepo	✅	✅
Yarn 2 PNP	✅	✅
Webpack5	✅	✅
Publishable (npm)	✅	❌ (ntm relies on "main")

See also

• https://stackoverflow.com/a/69554480/5490184

License