Node and NPM

Node

Node.js is a JavaScript runtime, so it basically allows you to run JS (outside of the browser)

NPM

NPM is the Node Package Manager and as it's name suggests, enables you to use third-party packages.

Your npm dependencies are specified in the file package.json

Generating package.json

You could write the package.json file by hand, but it's more convenient to generate it using the npm init command. You'll be asked several questions like your projects description etc. and at the end you'll get a package.json that looks something like this:

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{
  "name": "my-app",
  "version": "1.0.0",
  "description": "This is my app",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Michael König",
  "license": "ISC"
}

Installing new dependencies

You can install dependencies using the npm install <package name> (or short npm i <package name>) command.

The package will then be added as a dependency to the package.json file (under the key "dependencies") and it will also be downloaded into the node_modules folder.

To install a package and add it as a "devDependency" to your package.json (instead of a normal "dependency), run npm install --dev <package name> (or short npm i -D <package name>).

Theoretically, you could install all your dependencies as normal dependencies and not use dev-dependencies at all, but it's good practice to list packages, that are only necessary for development but not production (i.e. testing frameworks, code linters, code formatters), as dev-dependencies.

Installing dependencies listed in package.json

To install the dependencies listed in the package.json file, you can simply run npm install.

To install normal and dev dependencies, run npm install --dev

NPM scripts

You can create scripts in your package.json file:

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{
 ...
  "scripts": {
    "start": "node index.js"
  },
...
}

This script can be run using npm run start and it simply executes the file index.js using Node.js.