Node.js, npm and package.json

What is Node.js?

Node.js is an environment that lets you run JavaScript outside the browser, for example on your computer or on a server. It uses the same engine as Chrome (V8) and opens the door to building web servers, command-line tools and much more.

# Run a file with Node
node app.js

npm and package.json

npm (Node Package Manager) is Node's package manager. With it you install libraries that other people have published.

npm init -y          # creates a package.json
npm install lodash   # installs a dependency
npm install --save-dev jest  # development dependency

The package.json file describes your project: its name, version, dependencies and scripts.

{
  "name": "my-project",
  "version": "1.0.0",
  "scripts": {
    "test": "jest",
    "start": "node app.js"
  },
  "dependencies": {
    "lodash": "^4.17.21"
  }
}

The scripts are run with npm run <name> (or npm test, npm start for the special ones).

The node_modules folder (where dependencies are installed) is not pushed to the repository: it is regenerated with npm install from the package.json.

Examples

Read data from package.json (simulated)

const pkg = {
  name: "my-project",
  version: "1.0.0",
  scripts: { test: "jest", start: "node app.js" },
};
console.log("Project:", pkg.name, "v" + pkg.version);
console.log("Available scripts:", Object.keys(pkg.scripts));