Node.js and npm Prerequisites

What you will learn

• How to install Node.js and npm, and check that they work
• The few terminal commands you need for this course
• How to run a JavaScript file with the node command
• What npm, packages, package.json and node_modules are
• How npm scripts and npx save you typing

Express runs on Node.js, and you install Express with npm. This lesson gets both tools working on your computer, step by step. If you already use Node.js every day, skim the headings and jump to the practice section.

What are Node.js and npm?

Node.js is a program that runs JavaScript outside the browser. Your browser has a JavaScript engine built in. Node.js takes that same kind of engine (Google’s V8) and lets you use it on your computer or on a server.

npm stands for Node Package Manager. It does two jobs:

1. It is a huge online library (the npm registry) of free code that other people have shared. Express lives there.
2. It is a command-line tool that downloads that code into your project.

A package is a bundle of reusable code with a name, like express. When you “install a package”, npm downloads it so your code can use it. Installing Node.js also installs npm, so you get both in one go.

Step 1: Open a terminal

A terminal is a window where you control your computer by typing commands instead of clicking. A command is a short instruction such as “show me the files in this folder”. You type it, press Enter, and the terminal prints the result.

Tip: If you use VS Code, it has a terminal built in. Open it with View > Terminal or the Ctrl + ` shortcut. It opens in your project folder automatically, which is very handy.

The handful of commands you need

The terminal is always “standing” in one folder, called the current directory (or working directory). Commands run inside that folder.

Try it now. Make a folder for this course and move into it:

mkdir express-course
cd express-course
pwd

The last command prints the full path of your new folder, for example /Users/asha/express-course on macOS or C:\Users\asha\express-course on Windows.

Note: In this course, terminal commands are shown in blocks like the one above. Type them one line at a time and press Enter after each. Do not type any $ or > symbol you might see at the start of a line in other tutorials; that is just the terminal’s prompt.

Step 2: Install Node.js

Express 5 needs Node.js 18 or newer. Some lessons in this course use handy features from Node.js 20 and 22, so install the current LTS version.

LTS means Long-Term Support. It is the stable version that gets bug fixes and security updates for a long time. Always choose LTS for learning and for real projects.

The simple way: the official installer

1. Go to nodejs.org.
2. Download the LTS installer for your operating system.
3. Run it and accept the default options.
4. Close your terminal and open a new one, so it picks up the new program.

The flexible way: a version manager

A version manager lets you install several Node.js versions side by side and switch between them with one command. This is useful once you work on more than one project.

• macOS and Linux: nvm (Node Version Manager) or fnm.
• Windows: nvm-windows or fnm.

For example, with nvm on macOS or Linux:

nvm install --lts
nvm use --lts

If you are a complete beginner, the official installer is perfectly fine. You can switch to a version manager later.

Step 3: Check that it worked

Run these two commands:

node --version
npm --version

You should see two version numbers, something like this (yours will probably be different):

v22.11.0
10.9.0

The --version part is called a flag (or option). Flags change what a command does. Here it says “don’t run anything, just tell me your version”.

If the first number after the v is 18 or higher, you are ready for Express 5. If it is 22 or higher, every example in this course will work for you.

Common mistake: Seeing node: command not found or 'node' is not recognized. This almost always means the terminal was open before you installed Node.js. Close every terminal window, open a fresh one, and try again. If it still fails, restart your computer.

Step 4: Run JavaScript with node

The REPL: a JavaScript playground

Type node on its own and press Enter. You are now in the REPL (Read-Eval-Print Loop). It reads a line of JavaScript, runs it, prints the result, and waits for the next line.

> 2 + 3
5
> 'express'.toUpperCase()
'EXPRESS'
> .exit

Type .exit (or press Ctrl + C twice) to leave the REPL and get your normal terminal back.

Running a file

The REPL is fun for quick tests, but real programs live in files. Inside your express-course folder, create a file called hello.js with your code editor:

// hello.js
const name = 'Express learner';
console.log(`Hello, ${name}!`);
console.log('Node.js version:', process.version);

Now run it:

node hello.js

Hello, Express learner!
Node.js version: v22.11.0

That is all a Node.js program is: a JavaScript file that you run with node <file name>. console.log prints to the terminal instead of the browser console.

Note: Node.js does not have window, document or other browser-only objects, because there is no web page. Instead it has server-friendly tools, such as reading files and creating web servers. The process object you used above holds information about the running program.

Step 5: Understand npm and package.json

package.json: your project’s ID card

Every Node.js project has a file called package.json in its main folder. It records the project’s name, the packages it depends on, and handy commands. You create one with:

npm init -y

npm init normally asks you questions; -y means “yes to all the defaults”. You get a file similar to this (the exact fields vary a little between npm versions):

{
  "name": "express-course",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "type": "commonjs"
}

It is plain JSON: a text format of "key": value pairs inside curly braces. You can open and edit it in your code editor like any other file.

Installing a package

Let’s install a tiny package called picocolors, which adds colour to terminal text:

npm install picocolors

Three things happen:

1. npm downloads the package into a new folder called node_modules.
2. npm adds it to the dependencies section of package.json.
3. npm creates or updates package-lock.json.

Your package.json now contains something like:

{
  "dependencies": {
    "picocolors": "^1.1.1"
  }
}

The ^ (caret) means “this version or any newer version that is still 1.x”. That lets you get bug fixes without accidentally jumping to a big new version that might break your code.

Because package.json and package-lock.json describe everything, anyone can recreate node_modules by running npm install with no package name. That is why you never share or commit node_modules.

Using the package

Create colors.js:

// colors.js
import pc from 'picocolors';

console.log(pc.green('Success!'), pc.red('Error!'), pc.bold('Bold text'));

Before running it, make sure package.json has this "type" line, so Node.js understands the import keyword. If your file says "type": "commonjs", change "commonjs" to "module". If it has no "type" line at all, add one. The relevant parts look like this (other fields left out):

{
  "name": "express-course",
  "version": "1.0.0",
  "type": "module",
  "dependencies": {
    "picocolors": "^1.1.1"
  }
}

Note: A file must never have two "type" lines. Edit the existing one rather than adding a second.

Now run it:

node colors.js

You should see coloured words in your terminal. The "type": "module" line tells Node.js to treat your files as modern ES modules. The whole course uses this style. You will learn exactly what it means in ES Modules vs CommonJS in Express Apps.

Dependencies and devDependencies

Some packages are needed to run your app (like Express). Others are only needed while you develop it (like a testing tool). npm keeps them in two lists:

npm install express        # goes into "dependencies"
npm install -D nodemon     # -D: goes into "devDependencies"

Don’t run these yet; you will install Express properly in the next lesson.

Step 6: npm scripts and npx

npm scripts: shortcuts for long commands

The "scripts" section of package.json lets you name commands. For example:

{
  "scripts": {
    "start": "node hello.js",
    "colors": "node colors.js"
  }
}

Now you can run them like this:

npm start
npm run colors

start and test are special names that work with just npm start or npm test. Every other name needs npm run <name>. Real projects use scripts for starting, testing and building, so teammates don’t have to remember the exact commands.

npx: run a package without installing it globally

npx comes with npm. It runs a command from a package, downloading it temporarily if needed. For example, this runs the cowsay package once without adding it to your project:

npx cowsay "Hello Express"

npx asks for confirmation the first time it needs to download something. You will use npx occasionally for one-off tools.

Common mistakes

Common mistake: Running npm install in the wrong folder. npm looks for package.json in the current directory. Always cd into your project folder first, and check with pwd or ls that you see package.json.

Common mistake: Installing project packages globally with npm install -g express. Global installs are for command-line tools only. Packages your code imports must be installed inside the project, without -g.

Common mistake: Deleting package-lock.json to “fix” problems. It records exact versions for a good reason. If something seems broken, delete only node_modules and run npm install again.

Key takeaways

• Node.js runs JavaScript outside the browser. npm installs packages and comes with Node.js.
• Install the LTS version of Node.js. Express 5 needs Node.js 18+, and this course recommends 22 or newer.
• Check your setup with node --version and npm --version. Run a file with node file.js.
• package.json lists what your project needs; node_modules holds the downloaded code and is never committed.
• npm install <name> adds a dependency, -D makes it a dev dependency, and npm scripts give long commands short names.

Practice

1. Open a terminal, create a folder called playground, move into it, and print its full path.
2. Create math.js that logs the result of 7 * 6 and the current date with new Date(). Run it with node.
3. Run npm init -y in playground, then add a "start" script that runs math.js. Run it with npm start.
4. Install picocolors, delete the node_modules folder, then run npm install with no package name. Check that node_modules came back.

What’s next

Your tools are ready. Now let’s create a real Express 5 project. Continue with Installing Express 5 and Project Setup.