Putting It All Together

The full package manager pipeline:

1. Read manifest (package.json, Cargo.toml...)
2. If lockfile exists: use it. Else: SOLVE constraints to produce one.
3. For each (name, version) in lockfile:
   a. Already in cache? Skip download.
   b. Download from registry.
   c. Verify integrity hash.
   d. Extract.
   e. Run install scripts (preinstall, install, postinstall).
4. Optional: audit against vulnerability DB.
5. Set up bin symlinks (e.g. node_modules/.bin/*).
6. Print install summary.

Layers you've now built:

Real-world considerations:

• Workspaces / monorepos: multiple package.jsons in one repo, shared node_modules. Yarn workspaces, npm workspaces, pnpm.
• Peer dependencies: "I don't install this; my consumer must." Common for plugin ecosystems (eslint plugins peer-depend on eslint).
• Optional dependencies: install if available; ignore failure.
• dev vs prod: don't ship dev tooling to production.
• Aliases: npm install foo@npm:[email protected] — use bar pretending it's foo.
• Local file deps: "my-lib": "file:../my-lib" — path-based.

You now understand npm, yarn, pnpm, cargo, pip, gem, composer, NuGet, Maven — they're all the same underlying problem solved with slightly different tradeoffs.