Workspaces In Yarn

Yarn Workspaces

Notes from this come from the official Yarn article found here.

tl;dr Key Commands

Command	Function
yarn config set workspaces-experimental true	Initialises Workspaces

Introduction

Those who have tried splitting a project into multiple packages know how hard it is to make changes across multiple packages at one time. To make the process easier, some big projects adopted a monorepo approach, or multi-package repositories, which reduces the burden of writing code across packages.

Lerna

A tool to optimize workflow around managing multi-package repos.
Being a wrapper of a package manager, Lerna can't manipulate contents of node_modules efficiently, hence Workspaces.

Workspaces

Yarn Workspaces is a feature that allows users to install dependencies from multiple package.json files in subfolders of a single root package.json file, all in one go.

Enables faster, lighter installation. Also creates symlinks between Workspaces that depend on each other, and will ensure the consistencvy and correcvtness of all directories.

Example: Jest Workspace

| jest/
| ---- package.json
| ---- packages/
| -------- jest-matcher-utils/
| ------------ package.json
| -------- jest-diff/
| ------------ package.json
...

Example root package.json file. Generally kept as private.

{
  "private": true,
  "name": "jest",
  "devDependencies": {
    "chalk": "^2.0.1"
  },
  "workspaces": ["packages/*"]
}

How yarn install works with workspaces

Take the following two packages within Jest:

// First package.json
{
  "name": "jest-matcher-utils",
  "description": "...",
  "version": "20.0.3",
  "license": "...",
  "main": "...",
  "browser": "...",
  "dependencies": {
    "chalk": "^1.1.3",
    "pretty-format": "^20.0.3"
  }
}

// Second package.json
{
  "name": "jest-diff",
  "version": "20.0.3",
  "license": "...",
  "main": "...",
  "browser": "...",
  "dependencies": {
    "chalk": "^1.1.3",
    "diff": "^3.2.0",
    "jest-matcher-utils": "^20.0.3",
    "pretty-format": "^20.0.3"
  }
}

Running yarn install from anywhere within the projects yields the following:

| jest/
| ---- node_modules/
| -------- chalk/
| -------- diff/
| -------- pretty-format/
| -------- jest-matcher-utils/  (symlink) -> ../packages/jest-matcher-utils
| ---- package.json
| ---- packages/
| -------- jest-matcher-utils/
| ------------ node_modules/
| ---------------- chalk/
| ------------ package.json
| -------- jest-diff/
| ------------ node_modules/
| ---------------- chalk/
| ------------ package.json
...

Packages like diff, pretty-format and the symlink to jest-matcher-utils were hoisted to the root node_modules directory, making the installation faster and smaller. The package chalk however could not be moved to the root because the root already depends on a different, incompatible version of chalk.

Managing Dependecies

Run the installation within the desired package:

Note: that Workspaces don’t have their own yarn.lock files, and the root yarn.lock contains all the dependencies for all the Workspaces. When you want to change a dependency inside a Workspace, the root yarn.lock will be changed as well as the Workspace’s package.json.