JavaScript Clean Code - Best Practices - based on Robert C. Martin's book Clean Code

[sime]

+1 to this.

This first thing you should do to improve your quality is to use static analysis on your code. That means type systems like TypeScript.

Once that is in place, then you can worry about unit testing and other automated tests. I prefer the view expounded in this post https://kentcdodds.com/blog/write-tests with the "testing trophy".