Day 2 – Node.js: Runtime, nvm, and npm

Today's Focus

Understand what Node.js is and why it exists, install it using a version manager, and get comfortable with npm for managing JavaScript project dependencies.

What is Node.js?

JavaScript was originally designed to run only inside a web browser — it had no access to the filesystem, network sockets, or operating system. Node.js is a JavaScript runtime built on Chrome's V8 engine that runs JavaScript outside the browser.

Node makes it possible to write servers, CLIs, scripts, and build tools in JavaScript — using the same language for both frontend and backend code. It ships with a built-in HTTP module, and the npm ecosystem gives it access to hundreds of thousands of packages.

Node is not a language — JavaScript is the language. Node is the environment that executes it outside a browser.

Installing Node with nvm

Different projects require different Node versions. Installing Node directly risks the same global version conflict problem as Python. The solution is a version manager.

nvm (Node Version Manager) is the most widely used option. It installs Node versions into your home directory and lets you switch between them per-project.

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.7/install.sh | bash
source ~/.zshrc
nvm --version

Install and use a specific version:

nvm install 20          # install Node 20 (LTS)
nvm use 20
node --version          # v20.x.x
npm --version

Set a default version for all new shell sessions:

nvm alias default 20

Pin a version per project using a .nvmrc file:

echo "20" > .nvmrc
nvm use                 # reads .nvmrc automatically

n — a simpler alternative

n is a lighter version manager with a simpler interface. Install it once via npm, then use it to switch versions:

npm install -g n
n 20
node --version

nvm is generally preferred for teams because .nvmrc support makes version pinning automatic.

npm and package.json

npm is Node's package manager — it downloads packages from the npm registry and tracks your project's dependencies in package.json.

Starting a project

mkdir ~/projects/hello-node && cd ~/projects/hello-node
npm init -y

npm init -y creates a package.json with default values:

{
  "name": "hello-node",
  "version": "1.0.0",
  "main": "index.js",
  "scripts": {
    "start": "node index.js"
  }
}

Installing packages

npm install express          # adds to dependencies
npm install --save-dev jest  # adds to devDependencies (not needed in production)

npm creates:

• node_modules/ — the installed packages (never commit this)
• package-lock.json — the exact resolved versions (always commit this)

Add node_modules/ to .gitignore:

echo "node_modules/" >> .gitignore

Key npm commands

Writing and Running JavaScript with Node

Create index.js:

const name = 'Academy'
const languages = ['Python', 'JavaScript', 'Go', 'C#']

console.log(`Hello from ${name}!`)
console.log(`This course covers: ${languages.join(', ')}`)

languages.forEach((lang, i) => {
  console.log(`  ${i + 1}. ${lang}`)
})

Run it:

node index.js
# or
npm start

Tasks

• Install nvm following the instructions above. Close and reopen your terminal (or source ~/.zshrc), then verify nvm --version.
• Install Node 20 with nvm install 20. Check node --version and npm --version.
• Create a ~/projects/hello-node project with npm init -y. Install express as a dependency and inspect package.json and package-lock.json — note what each records.
• Add a node_modules/ entry to .gitignore. Delete node_modules/, run npm install, and confirm the packages come back — this is how a colleague restores your project after cloning it.
• Create a .nvmrc file pinning Node 20 in your project. Run nvm use and confirm it reads the file.
• Write a index.js script that defines a function, calls it with different arguments, and logs the results. Run it with node index.js.

Reading / Reference

• nvm README
• npm documentation
• Node.js about page
• The Odin Project: Introduction to Node