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Intro to Node

Pre-req / learning

Topics

  • Node
  • package.json
  • npm
  • module.exports / require (CommonJS)
  • export and import (ES6)
  • Environment variables

Node

JavaScript has two runtime environments

  • The browser runtime environment
  • The Node runtime environment.

Node is used for:

  • Creating server-side code
  • Code that is started using the terminal.
  • Code that runs without a Browser (no UI).

Suppose we had the following code in an app.js file:

// app.js
const rollDie = () => {
    return Math.ceil(Math.random() * 6);
}

We can run it in the Node runtime environment with the terminal command node app.js

Starting a Project

Node projects are often much more than just JavaScript files executed in the terminal. They can be just as complex as front-end applications which may utilize mutliple APIs and third-party services.

To create a new Node project, we'll be using npm (Node Package Manager). A typical workflow for starting a project looks like this:

  1. npm init -y to create a node project and create a package.json file (-y uses default settings)
  2. touch index.js to create your "entry point" file
  3. In package.json, and below the "test" script in "scripts", add a "start" script with the "start": "node app.js".
  4. Run npm start.

Node Package Manager

npm is a command-line tool that lets us download packages for our Node projects.

A package is a collection of files that we can download and import into our projects to add a specific functionality to our program.

Examples of NPM packages:

Installing Packages

  • npm install package-name is the syntax for installing packages for the current project.

    • Ex: npm install superheroes

  • npm i package-name is the shorthand syntax for installing.

    • Ex: npm i superheroes

  • npm i -D package-name uses the -D developer flag which installs packages as a developer dependency. Developer dependencies are not used in the program itself, but rather are used to aid in development.

    • Ex: npm i -D nodemon
    • Try updating the "start" script in package.json to use nodemon instead of node. Make a change to your .js file and see it automatically re-run!

Package.json

Installed packages live in a folder called node_modules and are listed in the package.json file:

  • Note the distinction between "dependencies" and "devDependencies".
  • Each package is listed with the version being used.
  • package.json files communicate to other developers which packages a project uses.
  • node_modules folders are typically NOT included in git repos. Instead, just the package.json file is needed and a developer can run the command npm install with no additional arguments and npm will look at the package.json file and install all dependencies listed there.

Require

We can import packages installed via npm using require(). When doing this, we ONLY provide the name of the package and require() will assume it is in node_modules.

// app.js
const superheroes = require('superheroes');
const randomHero = superheroes.random();
console.log(randomHero);

module.exports

We can create our own local modules as well!

  1. Create a utils.js file with functions and variables
  2. Export with module.exports
// utils.js
const rollDie = () => {
    return Math.ceil(Math.random() * 6);
}
const INSTRUCTOR_NAME = "BEN";
module.exports = {
    rollDie,
    INSTRUCTOR_NAME
}
  1. In app.js, import functions and variables using require and the relative path:
// app.js
const utilsExports = require("./utils"); // get the whole module.exports object
const { rollDie, INSTRUCTOR_NAME } = require("./utils"); // use destructuring

const roll = rollDie();
console.log(`${INSTRUCTOR_NAME} rolled a ${roll}`);

Environment Variables

Just like the window object in a browser, running Node applications have environment variables.

One of the most important is process.env.

console.log(process.env)

And we can set additional environment variables when we start our program like so:

  • port=8080 host='127.0.0.1' node index.js
console.log('The value of PORT is:', process.env.PORT); // 8080

Often, we won't set these values ourselves in our programs like this. Instead, cloud-hosting services will set these variables on our behalf. As a result, you will often see (and we will write) code that looks like this:

const port = process.env.PORT || 8000;
const host = process.env.HOST || '127.0.0.1'

Some other important values available in the Node runtime environment:

  • __dirname (the full path to the directory holding the current file)
  • process.argv (arguments included when starting a Node process)

Bonus Topic: https://www.npmjs.com/package/dotenv