I bought it because the bootcamp instructor recommended it and finished it in one day. I think instructor Kim Young-han filmed the lecture in one take in one day, so he worked really hard. I learned some of the web front-end with JavaScript and now I'm going into Node.js and dealing with the server side, so I needed basic concepts, so I listened to it. I was really touched by what he said during the lecture, that there are only materials explaining the functions, but they don't really explain why they are used and how they work. I'll listen to it over and over again.