From Jest to Vitest, Introduction to JS Test Code

If you use JS but find it difficult to explain why it works, this course provides the answer. From execution context, closures, and the event loop to Promise concurrency, prototypes, Virtual DOM, memory leaks, and bundle optimization—you won't just read about 18 chapters of advanced JS concepts; you'll learn by seeing them happen right before your eyes with a simulator. Code-based quizzes are provided for every chapter, and you can own it for life for the price of a single chicken dinner.

This introductory course is designed to help even those new to Git safely record file changes and understand collaboration workflows through GitHub. Rather than simply memorizing commands, the focus is on developing the intuition to read the current state using status, diff, and log, and to choose the appropriate action among add, commit, restore, reset, and revert based on the situation. The course begins by explaining why Git is necessary and the difference between simple file saving and version control. Afterward, you will practice creating a repository, committing a README.txt file, and observing how Git tracks changes. You will also learn the basics of backing up and sharing personal projects online by creating GitHub remote repositories and mastering the push and clone workflow. The intermediate section covers branches, merge, conflict, pull/push, PR, rebase, and stash. You will learn how to divide work into branches, merge changes, and read and resolve files when conflicts occur. Additionally, you will build the ability to handle common Git complications in professional settings by understanding PR-centered collaboration workflows and the differences between reset and revert. The final section covers GitHub Flow and operational branching strategies. It explains the process where feature branches are merged into the development branch and promoted to the production environment through QA, centered on the dev → stg → prd workflow. By covering hotfixes, release branches, tags, partial deployments, emergency fixes, and rollback decisions, this course is structured to help you understand how Git is operated in actual team development.

This course was created based on my personal experience passing the very first revised Information Processing Engineer practical exam, which had a pass rate of only 5.34%. The Information Processing Engineer practical exam can no longer be prepared for through simple memorization alone. In particular, the ability to read the execution flow of C, Java, Python, and SQL code to track results, as well as the ability to accurately distinguish short-answer concepts and write them as answers, has become crucial. This course is structured to help even beginners who are new to programming follow along step-by-step, covering everything from creating variable tables to tracking C, Java, Python, and SQL code, core practical terminology, and written exam subjects 1 through 5. Rather than being a video-centered course, this is a text-based course designed for fast reading and repeated review. It makes it easy to look up necessary parts again and focuses on practicing how to derive answers at the testing center by following the code and explanations directly. The 1st update covers the practical programming sections: C, Java, Python, and SQL. The 2nd update will organize core terms and concepts required for the short-answer practical questions and provide a "Stepper Simulator" to practice code tracking directly. The 3rd update will sequentially expand to cover written exam subjects 1 through 5. The Stepper Simulator is designed so that you don't just stop at reading explanations; you can understand how variable values change as the code executes line by line by following along yourself. If you have any questions while taking the course, please leave them in the Q&A. I will respond as quickly as possible to ensure your learning doesn't get stuck.

After studying JavaScript, starting TypeScript often leads to getting stuck on the question, "Why should I use these types?" rather than the new syntax itself. This course covers everything from basic types to unions, type narrowing, generics, keyof, Pick, and Omit in a connected learning path. Additionally, practice problems are provided as separate missions so you can directly apply what you've learned. After completing the course, you will be able to understand the causes of type errors instead of blindly hiding them, safely reduce repetitive types, and express the intent of your code through types.

Have you learned JavaScript but find yourself stuck when it comes to actual projects? I created this course for those who can use forEach but hesitate to use reduce, find asynchronous code a headache every time they see it, and build components without knowing the underlying reasons for their structure. This course doesn't just explain syntax. It focuses on "why we use it this way" to help you develop the coding intuition needed to jump straight into real-world work.

Hello, I am Gamja, a 4th-year frontend developer. Thinking back to when I first learned JavaScript, I remember many times when I felt like I understood everything while following along with YouTube videos or books, but my mind would go completely blank the moment I opened an empty editor. At first, I was just busy copying and pasting code I found through Googling. Because of that, when an error occurred, I didn't know where to start fixing it, and I would spend several days staying up all night in frustration. That’s when I realized a painful truth: writing one line of code yourself while understanding the principles is more valuable for your actual skills than copying someone else's code 100 times. Many beginners struggle with these concerns in front of the high wall of JavaScript: 🚨 "I made the screen look pretty with HTML/CSS, but I feel lost trying to make it move." 🚨 "I've memorized all the syntax for variables and functions, but I don't know how to combine them in practice." 🚨 "My head hurts just hearing terms like event bubbling or DOM manipulation." That is why I prepared this course. I have organized only the 'surest shortcuts' that I learned through countless trials and errors. While preparing the materials, I didn't list difficult development jargon. I boldly discarded the grammar found in thick textbooks that you won't even use right away. Instead, I will plant the core principles used in practice as naturally as breathing into your mind through intuitive everyday metaphors like 'conveyor belts' and 'paint palettes.' In this course, you won't just learn theory. As soon as you learn the theory, you will build four core UIs that you will inevitably encounter in frontend work—such as accordions, tab menus, and dark mode toggles—from scratch with me. After completing the course, you will no longer be someone who scrapes someone else's code and presses the run button while praying. You will be reborn as a real frontend developer who can design how to structure a screen on your own and write JavaScript code according to your intentions. I have included all of my practical know-how. Don't stop in front of an empty editor anymore. It's time to get started.

Are we truly utilizing HTML and CSS to their full potential? Before getting trapped in complex frameworks and JavaScript logic, we will directly implement everything from Whac-A-Mole to escape room games using only markup and styling—the essence of the web. Experience the power of 'fundamentals that aren't swayed by tools,' taught by an active developer with 4 years of experience.

In this course, you will learn how to test React applications.

Through this lecture, you will learn how to identify the overall types of front-end tests and how to write reliable tests by selecting the appropriate test for the situation.

I always had the question, 'Why on earth do we need to do frontend testing?' And with that doubt in mind, I mechanically wrote tests. But you will learn 'why we write tests' and 'how to write them according to different situations'.

In this course, you will create a Node.js application using test-driven development (TDD).

Learn how to add tests to Spring! Then, learn how to change the Spring design to make testing more natural.