What We’ve Learned

In this chapter, we saw how common async patterns can be implemented with minimal boilerplate using the right flow control functions. Async.js has become the number-one flow control library by offering a robust combination of collection iteration and task-wrangling methods. If you have a flow control problem, the odds are very good that Async.js has a solution. Or if you’re more of the do-it-yourself type, consider Step.

Isaac Schlueter, lead developer of the Node.js project, made a very small flow control library called Slide,^[43] which is used in npm. In Slide’s README, he wrote this:

You should use it as an example of how to write your own flow control utilities. You’ll never fully appreciate a flow control lib that you didn’t write yourself.

I hope that’s not true. Writing a flow control lib is a good exercise, but you shouldn’t have to reinvent the wheel just to see how it works. As the JavaScript ecosystem matures, flow control should become more widespread and more standardized. For the time being, if your application needs flow control, the important thing is to choose a good library and learn it well.