Modules, Dependencies and Environment Variables

Back to Node.js
Arjit Sharma
01 Min

As Node.js applications grow, everything can’t live in a single file. You need modular code, third-party libraries, and environment-based configuration.

Modules in Node.js

A module is just a reusable file that exports values (functions, objects, etc.) and imports them elsewhere. Node.js supports two system

CommonJS way - Node.js way

// math.js (exporting)
function add(a, b){
  return a + b;
}

function subtract(a, b){
  return a - b;
}

module.exports = { add, subtract};

// app.js (importing)
const { add, subtract } = require('./math');

console.log(add(5,3));// 8
console.log(subtract(10,4));// 6

ES Modules (ESM) - The Modern Way

Files must use .js with “type”: “module” in package.json, or use the .mjs extension.

{
"name":"my-app",
"type":"module"
}

// math.js (exporting)
export function add(a, b) { return a + b; }
export function subtract(a, b) { return a - b; }
export default function multiply(a, b) { return a * b; }

// app.js (importing)
import { add, subtract } from "./math.js";
import multiply from "./math.js";

console.log(add(5, 3));   // 8
console.log(multiply(4, 5)); // 20

Managing Dependencies with NPM

npm (Node Package Manager) is bundled with Node.js and is used to manage external libraries.

Installing a Package

npm install axios

Using a Package

import axios from "axios";

axios.get("https://api.github.com")
  .then(res => console.log(res.data))
  .catch(err => console.error(err));

Global vs Local Packages

  • Local → Installed per project (inside node_modules).
  • Global → Installed system‑wide, often for CLI tools (npm install -g nodemon).

Process Object

The process global gives access to runtime info, environment variables, and command‑line arguments.

console.log(process.env.PORT);     // Env variable
console.log(process.argv);         // Command-line args
console.log(process.cwd());        // Current directory
console.log(process.platform);     // OS platform

Example: Working with CLI arguments

node index.js hello world

process.argv.slice(2).forEach(arg => {
  console.log("Received:", arg);
});

Environment Variables with dotenv

Environment variables allow configuration without hardcoding values.

Install dotenv

npm install dotenv

Create a .env file

PORT=3000

Load Variables

require("dotenv").config();
console.log(`Running on port ${process.env.PORT}`);
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