> but does that mean it's a good idea?

Yes, to me it does. I love when variables have really tight scopes so I don't need to worry about if/how they are used throughout the rest of the program. Locality should be the default, not something that needs to be justified.

Creating a function is just unnecessary boilerplate if the code is not going to be reused. Functions are just named blocks with arguments. But if you don't need to name the block and don't need to reuse it with varying arguments, creating a function is just unnecessary.

Functional programmers are familiar with a concept called "let", which essentially gives you a way to introduce a variable and introduce a new scope just for that variable. This article is essentially just showing how to do that in JavaScript.