Callback best practices and control flow patterns

Now that you have met your first example of callback hell, you know what you should definitely avoid; however, that's not the only concern when writing asynchronous code. In fact, there are several situations where controlling the flow of a set of asynchronous tasks requires the use of specific patterns and techniques, especially if we are only using plain JavaScript without the aid of any external library. For example, iterating over a collection by applying an asynchronous operation in sequence is not as easy as invoking forEach() over an array; it actually requires a technique similar to recursion.

In this section, you will learn not only about how to avoid callback hell, but also how to implement some of the most common control flow patterns, using only simple and plain JavaScript.

Callback discipline

When writing asynchronous code, the first rule to keep in mind is to not abuse in-place function...