Summary

In this chapter, we explored in depth what modules are, why they are useful, and why we need a module system. We also learned about the history of modules in JavaScript and about the two module systems available today in Node.js, namely CommonJS and ESM. We also explored some common patterns that are useful when creating modules or when using third-party modules.

You should now be comfortable with understanding and writing code that takes advantage of the features of both CommonJS and ESM.

In the rest of the book, we will rely mostly on ES modules, but you should now be equipped to be flexible with your choices and be able to deal with CommonJS effectively if necessary.

In the next chapter, we will start to explore the idea of asynchronous programming with JavaScript, and we will examine callbacks, events, and their patterns in depth.