This shows the execution order given JavaScript's Call Stack, Event Loop, and any asynchronous APIs provided in the JS execution environment (in this example; Web APIs in a Browser environment)
Given the code
Picking the right architecture = Picking the right battles + Managing trade-offs
(by @andrestaltz)
If you prefer to watch video tutorials with live-coding, then check out this series I recorded with the same contents as in this article: Egghead.io - Introduction to Reactive Programming.