When yarn first came out in 2016, npm's problems (slow installs, no lockfile, non-deterministic dependency trees) made yarn the obvious winner. Two years later, npm 5 closed the gap significantly. Which should you use now?

Why yarn Was Born

The main problems with npm 3:

• No lockfile: different team members could get different dependency versions
• Slow: no parallel downloads, no caching
• Non-deterministic: npm install could produce different results

yarn solved all three at once:

• yarn.lock — deterministic dependency tree
• Parallel downloads + caching — dramatically faster
• Flat dependency resolution

npm 5+ Caught Up

npm 5 (Node.js 8 era) added package-lock.json and improved speed significantly. The gap narrowed considerably.

2018 Comparison

Feature	npm 5	yarn
Lockfile	package-lock.json	yarn.lock
Install speed	Fast	Fast
Workspaces	❌ (npm 7 added this)	✅ (built-in)
Offline mode	❌	✅
Output readability	OK	Better

Command Syntax

# Install
npm install            yarn
npm install --save     yarn add [package]
npm install --save-dev yarn add --dev [package]
npm install -g         yarn global add [package]

# Remove
npm uninstall          yarn remove

# Run scripts
npm run [script]       yarn [script]  (no 'run' needed)

# Update
npm update             yarn upgrade

Workspaces (monorepo)

yarn's built-in workspace support is a real advantage for monorepos:

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

# Install all workspace dependencies
yarn install

# Run a command in a specific workspace
yarn workspace my-package test

Lockfile Best Practices

Regardless of which you choose:

1. Commit your lockfile — package-lock.json or yarn.lock
2. Never mix npm and yarn in the same project — they'll generate conflicting lockfiles
3. Use the same package manager version across the team

My Recommendation (2018)

• New project: either works, just be consistent
• Monorepo: yarn (workspaces are far superior)
• Simple project without monorepo: npm 5 is fine

The most important thing is team consistency. Mixing package managers causes lockfile conflicts and non-deterministic installs.