Vanilla javascript is hit or miss for anything complex.

Using Typescript works great because you can still build out the interfaces and with IDE integrations the AIs can read the language server results so they get all the type hints.

I agree that the AI code is usually a pretty good starting point and gets me up to speed for new features fast rather than starting everything from scratch. I usually end up refactoring the last 10-20% manually to give it some polish because some of the code still feels off some times.