Node and npm

What this is

Node.js lets your computer run JavaScript outside of a browser.

npm is the package manager that comes with Node. It installs the libraries your project depends on.

Why it matters

Every modern web project — React, Next.js, Vite, Astro — needs Node to run locally.

When you run npm run dev, Node starts a local server on your computer so you can see the project in a browser before it is deployed. Without Node, you cannot run the project at all.

npm handles the dependencies. When you clone a project or scaffold one with AI, it will have a package.json file listing everything the project needs. Running npm install downloads all of it.

What to do

Install Node.js

Always install the LTS version (Long Term Support). It is the stable version recommended for most projects.

Download from nodejs.org.

After installing, close and reopen your IDE terminal, then check:

node -v
npm -v

You should see version numbers for both. Something like:

v20.11.0
10.2.4

If you see nothing or an error, close the terminal completely and reopen it.

What the key commands do

You will use npm install and npm run dev in almost every session.

The node_modules folder

When you run npm install, it creates a node_modules folder. This folder can be very large — sometimes hundreds of megabytes.

Do not commit node_modules to Git. A properly set up project will have a .gitignore file that excludes it automatically.

If you clone a project and it does not run, the first thing to try is:

npm install

This downloads the missing packages.

What package.json is

package.json is the project's manifest. It lists:

• The project name and version.
• The scripts you can run (like dev, build, start).
• The packages the project depends on.

When AI generates a project for you, it will create a package.json. Read it before running anything — it tells you exactly what the project is using.

Local development flow

npm install -> npm run dev -> open browser at localhost:3000 (or the port shown)

The terminal will show the local URL after npm run dev starts. Usually it is:

http://localhost:3000

Keep the terminal open while you work. Closing it stops the local server.

Common mistakes

• Installing Node but not restarting the terminal before checking node -v.
• Running npm run dev before running npm install — the project will fail.
• Closing the terminal while the dev server is running.
• Committing node_modules to Git — always check .gitignore exists.
• Installing the Current version of Node instead of LTS — stick to LTS for stability.