tessl/npm-yarn

Fast, reliable, and secure dependency management tool for JavaScript/Node.js projects

Overview

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Files

Project Management

Name: tessl/npm-yarn
Author: tessl

Commands for project initialization, script execution, and development workflow management.

Capabilities

Initialize Project

Create a new package.json file and initialize a new Node.js project.

yarn init [options]

-y, --yes               # Accept all defaults without prompting
--private               # Mark package as private (not publishable)

Usage Examples:

# Interactive initialization
yarn init

# Accept all defaults
yarn init -y

# Create private package
yarn init --private

# Create private package with defaults
yarn init -y --private

The init command prompts for:

Package name
Version (default: 1.0.0)
Description
Entry point (default: index.js)
Repository URL
Author
License (default: MIT)
Private status

Create Project from Template

Create a new project using a template package (create-* packages).

yarn create <starter-kit-package> [args]

Usage Examples:

# Create React app
yarn create react-app my-app

# Create Next.js app
yarn create next-app my-next-app

# Create Vue app
yarn create vue my-vue-app

# Create with additional arguments
yarn create react-app my-app --template typescript

# Equivalent to running:
# yarn global add create-react-app
# create-react-app my-app

Run Scripts

Execute scripts defined in package.json or run package binaries.

yarn run <script-name> [args]
yarn <script-name> [args]    # Shorthand for common scripts

# Built-in script shortcuts:
yarn start                   # Runs "start" script
yarn test                    # Runs "test" script  
yarn build                   # Runs "build" script

Usage Examples:

# Run custom script
yarn run dev
yarn run build:production

# Run with arguments
yarn run test -- --watch
yarn run build -- --mode production

# Shorthand for common scripts
yarn start
yarn test
yarn build

# List available scripts
yarn run

# Run script in specific workspace
yarn workspace my-package run build

Script Context:

Scripts run with:

node_modules/.bin in PATH
Access to all installed package binaries
Environment variables from .env files
Current working directory as project root

Execute Binaries

Execute package binaries directly without running them through npm scripts.

yarn exec <command> [args]

Usage Examples:

# Execute binary from node_modules/.bin
yarn exec eslint src/

# Execute with arguments
yarn exec webpack --mode production

# Execute binary that might not be in PATH
yarn exec @babel/cli --version

# Equivalent to npx
yarn exec create-react-app my-app

Run Node.js

Run Node.js with access to node_modules and yarn's environment.

yarn node [args]

Usage Examples:

# Run Node.js REPL
yarn node

# Execute JavaScript file
yarn node script.js

# Run with Node.js flags
yarn node --inspect script.js
yarn node --experimental-modules index.mjs

# Access to local modules
yarn node -e "console.log(require('lodash').version)"

Script Execution Context

When running scripts, yarn provides:

Environment Variables

# Package information
npm_package_name           # Package name from package.json
npm_package_version        # Package version
npm_package_description    # Package description

# Script context
npm_lifecycle_event        # Current script name being run
npm_lifecycle_script       # Current script command

# Paths
npm_config_cache          # Yarn cache directory
npm_config_prefix         # Global install directory
INIT_CWD                  # Original working directory

Script Hooks

Yarn supports lifecycle scripts that run automatically:

{
  "scripts": {
    "preinstall": "echo 'Before install'",
    "postinstall": "echo 'After install'",
    "prestart": "echo 'Before start'",
    "start": "node server.js",
    "poststart": "echo 'After start'",
    "pretest": "echo 'Before test'",
    "test": "jest",
    "posttest": "echo 'After test'"
  }
}

Lifecycle Order:

preinstall → install → postinstall
prestart → start → poststart
pretest → test → posttest
And so on for other scripts

Binary Access

Scripts automatically have access to:

All binaries from installed packages in node_modules/.bin
Global yarn binaries
System PATH binaries

{
  "scripts": {
    "lint": "eslint src/",           // Uses locally installed eslint
    "format": "prettier --write .", // Uses locally installed prettier
    "build": "webpack --mode prod"   // Uses locally installed webpack
  }
}

Script Best Practices

Cross-platform Commands

{
  "scripts": {
    "clean": "rimraf dist/",              // Cross-platform rm -rf
    "copy": "cpx 'src/**/*.json' dist/",  // Cross-platform cp
    "env": "cross-env NODE_ENV=prod node server.js"
  }
}

Chaining Commands

{
  "scripts": {
    "build": "yarn clean && yarn compile && yarn minify",
    "test:all": "yarn test:unit && yarn test:integration",
    "deploy": "yarn build && yarn test && yarn publish"
  }
}

Parallel Execution

{
  "scripts": {
    "dev": "concurrently 'yarn server' 'yarn client'",
    "test:parallel": "npm-run-all test:unit test:integration",
    "watch": "npm-run-all --parallel watch:*"
  }
}

Project Structure Integration

Yarn works seamlessly with common project structures:

Monorepo/Workspace Projects

# Run script in all workspaces
yarn workspaces run build

# Run script in specific workspace
yarn workspace @company/package-a run test

TypeScript Projects

# TypeScript compilation
yarn exec tsc
yarn run build  # if build script uses tsc

# Type checking
yarn exec tsc --noEmit

Modern JavaScript Projects

# ES modules with experimental flag
yarn node --experimental-modules index.mjs

# Module resolution
yarn node --es-module-specifier-resolution=node index.js

Install with Tessl CLI