Congratulations on reaching the final chapter of this book. If you have read everything that comes before, you now have a detailed understanding of the JavaScript language and know how to use it in Node and in web browsers. This chapter is a kind of graduation present: it introduces a handful of important programming tools that many JavaScript programmers find useful, and also describes two widely used extensions to the core JavaScript language. Whether or not you choose to use these tools and extensions for your own projects, you are almost certain to see them used in other projects, so it is important to at least know what they are. The tools and language extensions covered in this chapter are: ESLint for finding potential bugs and style problems in your code. Prettier for formatting your JavaScript code in a standardized way. Jest as an all-in-one solution for writing JavaScript unit tests. npm for managing and installing the software libraries that your program depends...