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Building a Server Framework from Scratch: Cloning the Express.js Engine

This course goes beyond simply using Express.js. You will rebuild its internal engine from start to finish, gaining hands-on experience with the real principles of how a server works. By directly creating each component of Express—such as routing, middleware, request–response objects, static file handling, and template rendering—you will grow as a server developer and truly understand how a framework operates at its core.

4 learners are taking this course

  • nhcodingstudio
실습 중심
백엔드
서버
웹개발
서버개발
JavaScript
Node.js
Express
backend
frontend

What you will learn!

  • Understanding the core principles of web server architecture by implementing Express.js from scratch

  • Rebuilding the entire Express.js architecture to fully grasp how it works

  • How the middleware chain and the next() function pass requests and maintain control flow

  • A structural analysis of how the request (req) and response (res) objects are composed and delivered

  • 정적 파일 서버를 안전하게 구현하기

  • Building stream-based logic to parse JSON and URL-encoded request bodies directly

  • Designing a RESTful router and constructing full CRUD APIs

  • Separating routers as modules and connecting them to the main app, just like express.Router()

  • Integrating the EJS template engine to render dynamic HTML

  • Implementing a structure to safely handle both synchronous and asynchronous errors within the middleware chain

  • Verifying and performing integration testing of the entire server using automated API test scripts

🚀 From "User" to "Builder" – Learning Core Principles of Server Development by Cloning Express.js

This course is a journey where we directly clone the engine of Express.js, one of the most widely used server frameworks in the web ecosystem, and implement its internal workings step by step.

I still remember when I first learned Node.js and Express. With just a single line like app.get() or app.use(), I could easily set up routing, middleware, static file handling, and template rendering. It felt magical. But at some point, a question came to mind: “Am I someone who truly knows how to build this, or just someone who knows how to use it?”

Express is incredibly convenient, but that convenience often hides its inner structure, making it difficult to understand how it really works. This course was created to fill that gap.

How is a routing system designed? Why are middleware executed in sequence? How are MIME types determined for static files? The essence of this course is to answer all these questions through direct implementation and hands-on practice.

By building Express yourself, you’ll go beyond just “knowing Express” and gain the foundational intuition of server development that allows you to naturally understand the structures of other frameworks like Fastify, Flask, Django, and Spring Boot.

This is not just about knowing how to use a framework. It’s about growing into someone who can design and implement the way a server works. Let’s begin this journey together—step by step, until you become not just a user, but a true builder.

👉 Key Features of This Course

📌 A project-based course where you clone the Express.js engine and implement all its core structures yourself
📌 No abstract theory—every principle is visualized and explained line by line in code
📌 Includes real-world implementations such as secure static file handling and robust error management
📌 Comes with all lecture materials and test scripts, so you can run and practice everything on your own
📌 Helps you grow into a developer who can build a server framework, not just use one


👉 Who This Course Is For

  • Developers who want to go beyond simply using Express.js and grow to the next level

  • Aspiring backend developers who want to understand server internals deeply

  • Learners who want to implement and learn the structural concepts of a web framework

  • Job seekers looking for a meaningful clone project to add to their portfolio

  • Developers experienced with Django, Flask, or Spring Boot who want to learn Node.js server architecture

  • Those who want to become developers who can explain how things work, not just use them

  • Frontend developers who want to better understand the flow between server and client

  • Beginners eager to build their own backend structure rather than just memorize functions

  • Career changers without a CS degree who want to gain solid fundamentals in web development

  • Frontend or full-stack developers who want to use JavaScript more deeply in backend projects


What You'll Learn

Designing the createApplication Function

Build the core controller structure that forms the entry point of the app object, including a settings store, router, and middleware registration. This ensures that a single app instance can drive the entire server.

Implementing the Middleware Chain

Implement the sequential execution flow of middleware using next(), visualize how each middleware intercepts and processes requests, and gain a foundational understanding—explained with the analogy of a hospital check-up flow.

Building a Static File Server
Use
fs.createReadStream() to stream files, automatically detect MIME types for the Content-Type header, and secure the server against path traversal attacks by adding safety logic.

Creating JSON and URL-Encoded Body Parsers

Receive HTTP request bodies as streams, accumulate data progressively using data and end events, then perform JSON parsing or URL decoding to build fully functional body-parsing middleware.

Designing Routers and Handling Dynamic Routes

Implement URL pattern matching such as GET /users/:id, place extracted values into req.params, and fully understand the path-based handler execution flow at the core of routing.

Building Error-Handling Middleware
Implement four-argument middleware (err, req, res, next), catch synchronous errors with try...catch, and safely capture asynchronous errors with Promise.reject() to establish a unified error-handling flow.

Implementing Template Rendering
Integrate the EJS template engine, implement the
res.render() method, and experience the complete process of server-side rendering by generating dynamic HTML from the server.

Recreating express.Router() Functionality

Implement a createRouter() function to create sub-router instances and connect them hierarchically to the main app, enabling modular management of large-scale API structures.

Improving Architecture

Apply the Singleton pattern and IIFE to prevent global state sharing, hide settings and internal modules, and strengthen security. Refactor by integrating middleware and separating concerns, creating an engine with real-world maintainability and scalability.

Automating API Testing

Use http.request() to send actual requests to the server, parse response bodies, and log results with status codes, building automated test scripts to ensure stability and reliability.

Before You Begin

Prerequisites and Notes

  • You should already be familiar with basic JavaScript syntax. This includes variable declarations, function definitions, array/object manipulation, and asynchronous handling with Promises.

  • A basic understanding of the Node.js environment and module system (such as CommonJS) will be helpful. Knowing how to run a local server and how require and module.exports work will make the process easier.

  • Prior experience using Express.js will help you grasp the concepts much faster. This course, however, focuses not on usage but on rebuilding and understanding the underlying mechanisms.

  • Please note: this course does not provide finished code or pre-built packages. Instead, you will implement everything step by step, writing code yourself to fully understand the structure and principles.

  • It is recommended to first take “Mastering Express.js: Part 1 – From Basics to Advanced [Beginner Track]”, where the foundational structure and usage of Express.js are covered. This course builds on that knowledge and focuses on implementing the internal architecture as an advanced track.


Recommended for
these people

Who is this course right for?

  • Developers who want to move beyond just using Express.js and grow to the next level

  • Aspiring backend developers who want to deeply understand how a server works internally

  • Learners who want to implement and learn the structural concepts of a web framework

  • Job seekers looking for a meaningful clone project to showcase in their portfolio

  • Developers experienced with other frameworks like Django, Flask, or Spring Boot who want to understand Node.js server architecture

  • Those who want to become developers who can explain how things work, not just use them

  • Frontend developers who want a clearer understanding of the flow between server and client in web development

  • Beginners who want to move beyond "just memorizing functions" and experience building their own backend structure

  • Career changers without a computer science degree who want to establish a solid foundation in web development

  • Frontend or full-stack developers who want to use JavaScript more deeply in real-world backend projects

Need to know before starting?

  • Basic JavaScript syntax

  • Experience with Node.js

  • Experience with Express.js (optional)

  • Knowledge of networking and HTTP concepts (optional)

Hello
This is

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Learners

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Reviews

4.6

Rating

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“우리가 공부하던 이 방식, 그대로 다른 사람에게도 전하면 어떨까?”

그 물음이 바로 우리동네코딩 스튜디오의 출발점이었습니다.

현재는 약 30명의 현직 개발자와 컴퓨터공학 전공 대학생들이 각자의 전문 분야를 맡아, 입문부터 실전까지 아우르는 커리큘럼을 직접 설계하고 강의합니다. 단순한 지식 전달을 넘어, 진짜 개발자의 시선으로 배우고 함께 성장할 수 있는 환경을 제공합니다.

“진짜 개발자는, 진짜 개발자에게 배워야 합니다.”

저희는 웹 개발의 전 과정을 처음부터 끝까지 체계적으로 다루되, 이론에 머무르지 않고 실습과 실전 중심의 피드백을 통해 실력을 키워드립니다.
수강생 한 사람, 한 사람의 성장을 함께 고민하고 이끌어가는 것이 우리의 철학입니다.

🎯 우리의 철학은 분명합니다.
"진정한 배움은 실천에서 오고, 성장은 함께할 때 완성된다."

개발을 처음 시작하는 입문자부터, 실무 능력을 키우고 싶은 취업 준비생, 진로를 탐색 중인 청소년까지.
우리동네코딩 스튜디오는 모두의 출발점이자, 함께 걷는 든든한 동반자가 되고자 합니다.

이제, 혼자 고민하지 마세요.
우리동네코딩 스튜디오가 여러분의 성장을 함께하겠습니다.


Welcome to Neighborhood Coding Studio!

Neighborhood Coding Studio was founded by a team of developers who studied computer science at top North American universities such as Carnegie Mellon, the University of Washington, the University of Toronto, and the University of Waterloo, and went on to gain hands-on experience at global tech companies like Google, Microsoft, and Meta.

It all began as a study group formed by computer science students across the U.S. and Canada, created to grow together by sharing knowledge, solving problems, and learning from one another.
Though we were attending different schools in different time zones, the experience was so meaningful that it led us to one simple thought:

“What if we shared this way of learning with others?”

That thought became the foundation of Neighborhood Coding Studio.

Today, we are a team of around 30 active developers and computer science students, each taking responsibility for their area of expertise—designing and delivering a curriculum that spans from foundational knowledge to real-world development.
We’re not just here to teach—we’re here to help you see through the lens of real developers and grow together.

“To become a real developer, you must learn from real developers.”

Our courses take you through the entire web development journey—from start to finish—focused on hands-on practice, real-world projects, and practical feedback.
We care deeply about each learner’s growth and are committed to supporting your path every step of the way.

🎯 Our philosophy is simple but powerful:
"True learning comes from doing, and true growth happens together."

Whether you're just getting started, preparing for your first job, or exploring your future in tech,
Neighborhood Coding Studio is here to be your launchpad—and your trusted companion on the journey.

You don’t have to do it alone.
Let Neighborhood Coding Studio walk with you toward your future in development.

Curriculum

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53 lectures ∙ (5hr 5min)

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