Thank you for your comment. This tutorial was written a while ago. It was one of my first large tutorials on Medium. I think it is more proper to see it in the context of about when it was written — that, minus 2 years prior to it.
This particular pyramid of hell was the result of writing nested Ajax calls in haste. This goes back way to jQuery days.
Today, this article is quickly becoming less relevant. . . the most complex solution I have seen to this was the redux-saga in React… for example to handle these cases, which will actually: 1. Let you fire as many separate requests as you want and 2. Cancel a previous request of the same kind when/if it is executed again.
Since reducers update the state, a copy is made, and eventually the conglomerate of “randomly called” events will not interfere with the state data integrity, regardless of when they return.
These examples are not necessarily the best coding practice, to begin with. But there was a transitional time when people got caught in this pattern.