Part 2. Production-grade Elm

In the next three chapters, you’ll learn techniques that can be found in most Elm applications in the wild: talking to servers, talking to JavaScript, and testing. Strictly speaking, not every Elm application needs these, but in practice, all three are used very widely.

In chapter 4, you’ll learn how to communicate with servers. This involves commands, a new concept within The Elm Architecture. Chapter 5 teaches how to communicate with JavaScript, which turns out to be very similar to communicating with servers. Chapter 5 also introduces the last foundational concept of The Elm Architecture: subscriptions.

Just as part 1 of the book ended with a chapter on how to make your code more reliable, so too does part 2, by teaching how to write automated tests for the code you’ve written in the preceding chapters. You’ll learn about Elm’s unit tests, fuzz tests, and how to test the user interface itself. By the end, you’ll know enough to use Elm professionally.