Getting Started with Node.js: What Is Server-Side JavaScript?

Today, rather than supporting so-called legacy browsers such as Internet Explorer 6 or 7 — which once held large market shares — a much greater emphasis is placed on responsive design, cross-browser compatibility, and multi-browser support.
As the environments used to browse the internet evolved, development environments also changed alongside them.
Apple’s iOS, used on the iPhone, chose not to support Flash, which had once been standard on desktop browsers, and Android also gradually phased out Flash support. As smartphones became widespread, web design standards shifted to prioritize mobile compatibility, leading to a rapid decline in Flash-based web content.

This is where JavaScript began attracting major attention.
As Flash — which had originally been responsible for rich interactive content — was phased out, the industry shifted toward recreating those experiences using JavaScript instead.

As a result, many JavaScript libraries emerged. Among them, the most well-known is jQuery, which became a standard tool in web production environments.
Even jQuery underwent a major shift with the release of version 3.x in 2016, changing its direction by dropping support for legacy browsers and focusing more heavily on lightweight performance and efficiency.

In recent years, a wide variety of libraries, frameworks, and runtime environments have been developed to improve both development efficiency and performance.
Among them, one technology that attracted particular attention is Node.js, which enables JavaScript to run on the server side.

Node.js is often referred to as “server-side JavaScript.”
So what exactly is it, what characteristics does it have, and how does it differ from traditional web servers such as Apache?
These are the key points we will focus on.

Node.js is one of the environments used to execute JavaScript on the server side.
Today, when people refer to “server-side JavaScript,” Node.js is generally the most representative example.

The phrase “an environment for running JavaScript on the server” can feel a bit abstract at first. Personally, I found it easier to understand by comparing Node.js with traditional web servers such as Apache or nginx.

In a simplified sense, you could think of Node.js as being able to “serve a role similar to Apache.”
However, their characteristics and strengths are quite different, so Node.js is not a complete replacement in every situation.

The C10K problem refers to a situation where a server becomes overloaded and crashes even when the hardware specifications themselves are not the issue.
This became a major challenge in web server architecture, and Node.js emerged as one of the solutions to address it.

In traditional Apache-based architectures, one thread is created for each client request being processed.
With this approach, when the number of clients increases significantly, the number of threads also increases proportionally, resulting in heavy memory consumption. This is known as synchronous I/O.

As a solution, event-driven architectures were introduced, allowing processing to occur using a single thread.
An event-driven model handles many requests by repeatedly looping through them within a single thread.
This approach is also adopted by nginx and is referred to as asynchronous I/O.

However, another issue arises when performing heavy processing tasks: the entire process can slow down while waiting for those tasks to complete.
The idea behind non-blocking processing is to continue handling other tasks while waiting for time-consuming operations to finish.

Node.js adopts asynchronous, non-blocking I/O architecture.

About Node.js – Official Website
Beginner-Friendly: Understand What Node.js Is in 3 Minutes
Blocking I/O / Non-Blocking I/O

So, what exactly can Node.js do? What is it good at, what are its weaknesses, and how can it be used?
Let’s take a closer look.

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Node.js has a framework called Express.
Express makes it possible to build applications with Node.js quickly and with minimal setup.

Because it supports View Engines, developers can create web applications using Node.js while also building the visual interface with HTML templates.

Official Express Website

Companies and organizations such as PayPal and NASA have adopted Node.js for backend development.
The fact that such major companies and institutions are actively using Node.js suggests that it has the potential to become an important mainstream technology for the future of the web.

PayPal Migrates Backend from Java to JavaScript
NASA Open API

In this article, we explored the key concepts necessary for understanding Node.js.
Node.js originally emerged as one of the solutions to the C10K problem, but that was already several years ago. Today, it feels as though Node.js has naturally become one of the standard options available in modern web development.

In the next article, we will build an environment where Node.js can run on a server using nginx.