Introduction

Callbacks are the low-level building blocks of asynchronous programming in Node.js, but they’re far from being developer-friendly. In fact, in the last chapter, we learned techniques to implement different control flow constructs using callbacks, and we can say that they’re really complex and verbose compared to the (low) level of complexity of the tasks they try to accomplish. In particular, serial execution flow, which is the predominant control flow structure in most of the code we write, can easily lead an untrained developer to write code affected by the callback hell problem. On top of that, even if properly implemented, a serial execution flow seems needlessly complicated and error prone. Let’s also remember how fragile error management with callbacks is; if we forget to forward an error, then it just gets lost, and if we forget to catch any exception thrown by some synchronous code, then the program crashes. And all of this without considering that Zalgo is always breathing down our necks.