Package Registry

Think of a package registry as an app store for code.

It is a server that provides the metadata and artifacts for a package manager to install.

The most popular package registry is the public npm registry, which JavaScript package managers use for the bulk of their content.

What happens when you run npm install

When you run this command in your terminal: npm install react

Here's what happens behind the scenes:
Your terminal
    │
    │  "Hey registry, I want to use react"
    │
    ▼
registry.npmjs.org  (the public npm registry)
    │
    │  "Here's react's metadata + a download link"
    │
    ▼
Your project's node_modules/react/
    (package downloaded and saved locally)

The registry is just a server that:

1. Stores every version of every published package
2. Responds to requests like "give me react version 18.2.0"
3. Authenticates publishers (so only you can update your own packages)
4. Verifies integrity (checks that the file you downloaded hasn't been tampered with)