NodeJS

NPM

JavaScript and NodeJS Fundamentals

NPM

What is NPM
Creating a package
Package.json
Installing a package
Package-lock.json

When you write code , you will often need to use code written by other people; for example, libraries to help you work with dates, colors, servers, or almost anything else.

Instead of downloading and copying files manually, you can use a package manager.

A package manager is a tool that:

downloads packages
keeps track of which packages your project needs
makes sure everyone on your team has the same versions of the packages

What is NPM

In the NodeJS world, the most popular package manager is NPM, which stands for Node Package Manager.

You get NPM automatically when you install NodeJS.

You can check if you have NPM by running this in your terminal:

npm -v

This prints the version of NPM you have, like:

10.2.1

Creating a package

In NodeJS, a package is just a directory with a package.json file in it.

Let’s create one step by step.

Make a new folder for your project:
```
mkdir my_project
cd my_project
```
Run this command:
```
npm init
```

This starts an interactive setup, asking you questions like the name of your project, version, description, etc.

If you don’t want to answer everything and just accept the defaults, you can use:

npm init -y

After running it, you will see a new file in your folder called:

package.json

package.json

The package.json file is just a JSON file that stores metadata about your project.

Here’s an example:

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

A few important fields:

name: the name of your package
version: the current version
main: the entry point file (like index.js)
scripts: commands you can run (like npm start)
dependencies: lists all the packages your project depends on

Installing a package

Let’s say you want to use a certain package called picocolors to add colors to your terminal output.

You can install it by running:

npm install picocolors

You can now use it in your project. Make a index.js file with

const pico = require('picocolors')

console.log(
  pico.green("This text is green!")
)

and try running it. The terminal should print a colored version of the text.

What did NPM do ?

It downloaded the package and stored it in a subfolder called node_modules/

it added an entry under dependencies in your package.json
it updated the package-lock.json file

What is package-lock.json ?

package-lock.json

This file is automatically created by NPM.

You might wonder, if we already have package.json, why do we need another file? Here is the reason:

package.json just says which version range of a package your project needs. Example:
```
"dependencies": {
  "picocolors": "^1.1.0"
}
```
The ^1.1.0 means “any version that is compatible with 1.1.x”, so it’s flexible.

package-lock.json freezes the exact versions of every single package and their sub-dependencies, so that everyone who installs your project gets the exact same working setup.

Why is this important?

If you work on a team, or you deploy your project to a server, or you come back to it in the future, you want to make sure it still works the same way. If the packages have been updated and you reinstall without a lock file, you might get a slightly different version that behaves differently.

By keeping the package-lock.json in your project, NPM will always install the exact versions listed there, ensuring that everyone has the same environment.

package-lock.json locks everything to a very specific version, to make the project more reproducible on other machines.

But if your package needs to be used by many people, you might instead choose not to commit it, so that NPM only finds the package.json file and it's allowed to install automatically the latest versions that are allowed in that file.

But these are things you should worry about later, once you start publishing your own code. For now, we introduced the basics of NPM just to allow you to find and use the libraries published by other developers in your projects.