I am a junior developer currently working as a front-end developer. I thought I knew it well, but after watching this lecture, I found myself knowing it here and there. Now, I will write my course review. I am writing this review after listening to all four lectures, from the JavaScript beginner course to the ES6 advanced course. I think the best course review is when you can write about things that you couldn't write because you had vague knowledge. For example, by knowing the argument value that will receive the parameter value as this after the map, forEach, and filter functions, I was able to finish the time complexity of (n2) by repeating the loop twice, and as the concept of call, apply, and bind became clearer, I was always confused about this, but when I was confused, I could directly bind this when calling the function and handle it. And as for the concept of scope, while listening to the in-depth course, I found it step by step, and if it is not there, I look for __proto__, and if it is not there, I look for __proto__ in the lower part, etc. I don't know if this expression is right, but I was really blessed while listening to Youngbo's lecture... And last night, while implementing csr directly in vanilla, I felt the fun of learning about things that I would not have even known the principles of in the front-end framework, such as inheriting built-in objects for class events and processing them. Certainly, even people in the team said that my code has suddenly become surprisingly clean. They told me stories. For those of you who are thinking about taking the course, this is a course that you will not regret spending money on. Especially for those of you who want to know and use it for sure, you will feel that there are many more convenient, better, and more efficient built-in functions than the ones you used every day. Don't hesitate, I recommend that you purchase all of Youngbo's lecture series and listen to them all. You will feel that the quality of your code will change and your way of thinking will change. I am proud of it.