I integrated Prettier, ESLint and Travis CI with Hello, Goodbye.
Before someone commits, Prettier automatically formats their code to fit in with the other code. Travis CI automatically lints the code, and checks that it is written well using ESLint.
I will write some tests in the next day, so I don't have to manually test each new version (which takes about an hour).
Code quality is important, and I'm already happy, because it made my code much more friendly to write.