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#javascript

Yarn

Yarn is a package manager for JavaScript and TypeScript. It is a alternative to npm

Workspaces

Yarn provide a solution to manage Monorepo - Yarn Workspaces

  • Basically a Monorepo manager
  • in comparison with Lerna.js Yarn Workspaces are low-level

Setup from scratch 

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mkdir yarn-workspaces-sample && cd yarn-workspaces-sample && touch package.json

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// package.json
{
  "private": true,
  "workspaces": ["packages/*"]
}

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mkdir packages && mkdir packages/server && mkdir packages/utils

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cd packages/utils && yarn init -y
cd ../server && yarn init -y

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cd ../utils && touch main.js

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// packages/utils/main.js
function greeting(name) {
  console.log(`Hello, ${name}`);
}

module.exports = {
  greeting,
};

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cd ../server && touch main.js

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// packages/server/main.js

const { greeting } = require("utils");

greeting("byte");

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// packages/utils/package.json
{
  "name": "utils",
  "version": "1.0.0",
  "main": "main.js", // index.js ==> main.js
  "license": "MIT"
}

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// packages/server/package.json
{
  // ...
  "dependencies": {
    "utils": "1.0.0"
  }
}

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yarn install

yarn install will link dependency utils to server

After installing let’s check that server has workspace dependency utils:

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yarn workspaces info

should print this:

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{
  "server": {
    "location": "packages/server",
    "workspaceDependencies": ["utils"],
    "mismatchedWorkspaceDependencies": []
  },
  "utils": {
    "location": "packages/utils",
    "workspaceDependencies": [],
    "mismatchedWorkspaceDependencies": []
  }
}

Add scripts

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// packages/server/package.json
{
  // ...
  "scripts": {
    "dev": "node main.js"
  }
}

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// /package.json (root)
{
  "scripts": {
    "server:dev": "yarn workspace server dev"
  }
}