I first took React and Node.js through CodingApple, but it was disappointing that the method of linking the two was not done properly and there was no decryption content at the login. Above all, I was having too much trouble linking them and was about to give up when I found this lecture. It's really great ㅠㅠ The only thing that didn't work because the library changed was that in the mongoose part, useNewUrlParser, useUnifiedTopology, useFindAndModify, and useCreateIndex were not supported in mongoose version 6 or higher, so these items had to be deleted. Most of the errors were asked and solved by the community members here, so I was able to proceed easily. Above all, I feel really good because I feel like I've gained a lot of backend knowledge. I was really depressed because I cut off 300,000 won from a fast-paced university and talked nonsense, but now I can properly proceed with the project ㅠㅠㅠㅠ Thank you so much.