What Is Node.js? JavaScript on the Server Side

01What Is Node.js?

To answer what Node.js is, we first need to correct a misunderstanding: Node.js is not a programming language or a framework. The language is still JavaScript; Node.js is the environment that can run that language outside the browser.

For many years JavaScript lived only in the browser. Node.js, which appeared in 2009, brought Chrome's JavaScript engine V8 to the server and gave the language abilities such as reading files, making network connections and accessing databases. As a result, the same language could be used on both the front end and the back end.

npm, which comes with Node.js, gives access to one of the world's largest open-source package registries. Used to start a project, add dependencies and run scripts, this tool makes Node.js indispensable not only for people who write servers but for front-end developers too.

If you do not yet know the basic concepts of JavaScript, we recommend first reading the what is JavaScript article; the code you write in Node.js uses the same syntax.

02How Does the Event-Driven Model Work?

The most distinctive feature of Node.js is the event loop model. In some traditional server designs, a separate thread is opened for each request, and that thread waits until the database responds. Node.js does not wait: it starts the request, asks to be notified when the response arrives, and meanwhile handles other requests.

You can compare it to a restaurant waiter. The waiter passes the order to the kitchen and does not stand at the table until the food is cooked; they look after other tables and serve the dish when it is ready. A single waiter can cover many tables in an environment with a lot of waiting.

This model is called non-blocking I/O. It is what makes Node.js efficient in applications full of tasks that involve waiting, such as database queries, file reads or requests to another service.

import { readFile } from "node:fs/promises";

console.log("1. Reading started");

const icerik = readFile("notlar.txt", "utf8")
  .then(metin => console.log("3. Dosya okundu:", metin.length, "karakter"));

console.log("2. This line runs without waiting for the file");

03What Is Node.js Used For?

The answer to what Node.js is used for is broad; but the areas where it is strongest share a common trait: many concurrent connections and plenty of waiting. Typical uses are:

• REST and GraphQL APIs: backend services that serve data to mobile apps and web front ends
• Real-time applications: live chat, notifications, order tracking, collaboration screens
• Integration services: intermediary layers that move data between marketplace, shipping, payment and accounting systems
• Webhook receivers: endpoints that receive and process events from external systems
• Command-line tools and build processes: developer tools such as npm and Vite also run on Node.js
• Server-side rendering: generating pages on the server with frameworks such as Next.js

A Real-Life Scenario

Think of a hotel software system: the reception screen, the online booking form and the sales channels must all see the same room availability. When a booking comes in, the other screens need to update within seconds. Such instant notifications are the natural territory of event-driven servers, which can hold many open connections with few resources.

04Node.js Backend and Express.js

The best-known helper tool for Node.js backend development is Express.js. Express is a small, flexible web framework that makes it easier to manage routes, requests and responses, and middleware. Fastify, NestJS and Koa are other options used for the same purpose.

The example below sets up a simple API endpoint that returns a product list. In a real project, this data would have to come from a database, and authentication and error handling would have to be added. If you want the API concept in detail, our what is an API article explains the REST logic step by step.

mkdir urun-api && cd urun-api
npm init -y
npm install express

const express = require("express");
const app = express();
app.use(express.json());

const urunler = [
  { id: 1, ad: "Olive oil" },
  { id: 2, ad: "Thyme honey" }
];

app.get("/api/urunler", (req, res) => {
  res.json(urunler);
});

app.listen(3000, () => {
  console.log("API is running at http://localhost:3000");
});

05Strengths and Weaknesses

Like any technology, Node.js shines at certain jobs and is not the right choice for others. The decision should be made by the application's workload, not by slogans.

Solutions for Heavy Computation

Jobs that keep the processor busy for a long time can be handed off to worker threads in Node.js, to a separate job queue, or to a service written in a language better suited to the task. That way the main application keeps responding to user requests.

Package Security

The npm ecosystem is a big advantage, but every dependency also carries risk. Basic precautions are choosing actively maintained, widely used packages, checking for known vulnerabilities regularly with npm audit, and keeping the lock file (package-lock.json) in version control.

06Node.js in Integrations

A business's software rarely works alone. The website takes an order, shipment details go to the shipping company, an invoice lands in the accounting program, and stock on the marketplace is updated. The intermediary layers that move data between these systems suit the waiting-heavy nature of Node.js very well.

For example, an order notification from an external service is received at an endpoint, verified, written to the database and passed on to the relevant systems. Building such flows reliably also requires details such as retries, logging and error notification; the hard part of integration work is not the code but these details.

On our marketplace integration and shipping integration pages, we explain how data flows from order to delivery for marketplace and shipping connections in particular. Whatever technology it is written in, the measure of a good integration is that it eliminates manual data entry.

07Getting Started with Node.js

To get started, just install the current LTS version for your operating system from nodejs.org. LTS is the release line that receives long-term support and is recommended for live projects. After installation, you can verify the version in the terminal with the commands below.

1. Start with core topics such as the module system and file and path operations.
2. Get to the level where you can read asynchronous code comfortably with Promises and async/await.
3. Write a small API with Express, then connect a database.
4. Learn environment variables, error handling and logging.
5. Keep your code in version control and commit in small steps.

node -v
npm -v

Do Not Neglect Version Control

Tracking the project with Git from day one makes it easier to roll back a bad change and to work as a team. For the basics, see our what is Git article.