sample-monorepo

Sample monorepo setup with yarn workspaces, typescript, and lerna.

Setup explained

Tooling

• Monorepo is installed using yarn.

  • Packages are automatically linked together, meaning you can do cross-package work within the repo.
  • devDependencies are common, and only appear in the root package.json. Easier to manage and upgrade.
  • Each package has its own scripts and dependencies. They are being installed in the root node_modules, using the same deduping mechanism yarn uses for single packages.
  • Adding new packages is as simple as dropping an existing package in the packages folder, and re-running yarn.

• Monorepo scripts are being executed using lerna.

  • lerna publish - multi-package publishing.
  • lerna run - running package scripts.
  • lerna updated - shows changed packages (since last tag).

• Sources and tests are written in strict TypeScript.

  • Common base tsconfig.json.
  • @ts-tools/node is used to run code directly from sources.

• Testing is done using mocha and chai.

  • Light, battle-tested, projects with few dependencies.
  • Can be bundled and used in the browser.

Included sample packages

• @sample/components

  • React components library.
  • Built as cjs (Node consumption) and esm (bundler consumption).

• @sample/app

  • React application.
  • Uses the @sample/components package (also inside monorepo).
  • Built as cjs (Node consumption) and umd (browser consumption).

• @sample/server

  • Express application.
  • Uses the @sample/app package (also inside monorepo).
  • Listens on http://localhost:3000 (client only rendering) http://localhost:3000/server (SSR rendering).
  • Built as cjs (Node consumption).

Basic structure and configurations

.github                  // CI flow configuration (GitHub Actions)
packages/
  some-package/
    src/
      index.ts
    test/
      test.spec.ts
    LICENSE              // license file. included in npm artifact
    package.json         // package-specific deps and scripts
    README.md            // shown in npmjs.com. included in npm artifact

.eslintignore            // eslint (linter) ignored directories/files
.eslintrc                // eslint (linter) configuration
.gitignore               // github's default node gitignore with customizations
.mocharc.js              // mocha (test runner) configuration
lerna.json               // lerna configuration
LICENSE                  // root license file. picked up by github
package.json             // common dev deps and workspace-wide scripts
README.md                // workspace-wide information. shown in github
tsconfig.json            // common typescript configuration
yarn.lock                // the only lock file in the repo. all packages combined

Dependency management

Traditionally, working with projects in separate repositories makes it difficult to keep versions of devDependencies aligned, as each project can specify its own devDependency versions.

Monorepos simplify this, because devDependencies are shared between all packages within the monorepo.

Taking this into account, we use the following dependency structure:

• devDependencies are placed in the root package.json
• dependencies and peerDependencies are placed in the package.json of the relevant package requiring them, as each package is published separately

New devDependencies can be added to the root package.json using yarn:

yarn add <package name> --dev -W

Some packages depend on sibling packages within the monorepo. For example, in this repo, @sample/app depends on @sample/components. This relationship is just a normal dependency, and can be described in the package.json of app like so:

  "dependencies": {
    "@sample/components": "<package version>"
  }

Deployment

yarn lerna publish will publish new versions of the packages to npm.

Lerna asks for new version numbers for packages that changed since last release and their dependencies. Every package has a prepack script which automatically runs build prior to packing.

yarn lerna publish --force-publish will force a release of all packages, regardless of which ones actually changed.

Deployment of app/server assets to any actual production servers is not shown.