Testing is more expensive up front and in maintenance than type annotations. A test suite comprehensive enough to replace type annotations would have an ass load of assertions that just asserted variable type; if you were involved in early pre-TS Node, you remember those test suites and how they basically made code immutable.

> (2) it regularly missed deeper problems

This is a skill issue. If your types do not match runtime behavior and you choose to blame the programming language rather than your usage of it, that's on you. There are a lot of unsafe edges to TS, but a diligent and disciplined engineer can keep them isolated and wrapped in safe blocks. Turn off `any`, turn on all the maximal strictness checks, and see if your code still passes, because if what you said about infinite scroll is true, it won't.

Yeah, I agree, and the thing is, you're going to write automated tests whether you're developing in JavaScript or TypeScript so the extra cruft of TypeScript seems even less worthwhile.

The argument I've heard people put forward is that JS is fine for small projects or a couple of developers but doesn't scale to large projects or teams. I don't know how large large is, but I've worked on a project with around 30 devs where the front-end was all JavaScript and everyone was touching it and, sure, that project had some problems, but the root cause of those problems wasn't using JavaScript.