Ask HN: (2019) What are state of the art tools for front end Web developers?

I saw someone put this question out a few years ago so I thought it might be interesting to get a 2019 take.

Libraries, Frameworks, Testing tools, Continuous Integration tools, Automation tools, Compilers, Debuggers, Profilers, Collaboration tools...

previous discussion: https://news.ycombinator.com/item?id=9587149