Please explain in detail step by step. ㅎㅎ I like the lecture. But there are two things I regret. ㅜㅜ 1. It's not a problem with the lecture, but right after the lecture, TS version 4 came out, so there are some differences from the latest Ts grammar. 2. If you had left a commit for each lecture on GitHub for the project, it would have been easier to follow the lecture and check the changed code. ㅜ