The async library

If we take a look for a moment at every control flow pattern we have analyzed so far, we can see that they could be used as a base to build reusable and more generic solutions. For example, we could wrap the unlimited parallel execution algorithm into a function which accepts a list of tasks, runs them in parallel, and invokes the given callback when all of them are complete. This way of wrapping control flow algorithms into reusable functions can lead to a more declarative and expressive way to define asynchronous control flows, and that's exactly what async (https://npmjs.org/package/async) does. The async library is a very popular solution, in Node.js and JavaScript in general, to deal with asynchronous code. It offers a set of functions that greatly simplify the execution of a set of tasks in different configurations and it also provides useful helpers for dealing with collections asynchronously. Even though there are several other libraries with a similar goal, async...