So then they put it into lib only to find that they have to manually require it. Then later realize that this also means they now have to reboot their server any time they change the file (after a painfully long debugging time of "why what aren't my changes working?", because their lib folder classes are now second-class citizens). Then they go down the rabbit hole of adding lib to the autoload paths, which burns them because rake tasks then all get eager loaded in production. Then they inevitably realize anything inside app is autoloaded and make an app/lib per Xavier's advice.

I think the symmetry of the naming between lib and app/lib will lead a fresh Rails developer to seek out the answer to “Why are there two lib directories?", and they will become illuminated. And it will prevent them from seeking the answer to “How do I autoload lib?” which will start them on a rough path that leads to me advising them to undo it.

Now consider we want to handle numbers in our known value set: const KNOWN_VALUES = Object.freeze(['a', 'b', 'c', 1, 2, 3]) function isKnownValue(input?: string | number) { return typeof(input) === 'string' && KNOWN_VALUES.includes(input) } Uh oh! This TypeScript compiles without errors, but it's not correct. Where as our original "naive" approach would have worked just fine. Why is that? Where is the breakdown here? It's because TypeScript's type system got in the way of the developer's initial intent. It caused us to change our code from what we intended to what it allowed. It was never the developer's intention to check that input was a string and a known value; the developer simply wanted to check whether input was a known value - but wasn't permitted to do so.

Furthermore, JSX encourages bad non-dry code. Having seen a lot of JSX over the past few months, its encourages copypasta coding.