简单的Node / Express应用程序，功能编程方式（如何处理JavaScript中的副作用？）

There are many good articles about the theory of functional programming in JavaScript. Some even contain code examples showing the difference between imperative/object-oriented programming and declarative/functional programming. But I have found none that show, with simple JavaScript code examples, how to handle side-effects in a web app. No real world application can entirely avoid side-effects (database calls, logging to console, saving to a file, drawing to the screen etc.) and I have a hard time figuring out how it is done in practice.There are many good articles about the theory o