Switches - disallow fall through

Hey,

I’m not sure if this kind of things is outside of the scope of the language (is it “only” supposed to add types to JS, or is it an opportunity to improve other areas too?), but I thought I would suggest.

First, I love that you force exhaustive switches! Something that feels sorely lacking in TS.

I am wondering if you could also error if a case doesn’t contain a break/return statement. This is a common source of errors in switch statements, and the fall-through behaviour is generally considered a bad design decision in JS. Disallowing fall through will prevent bugs, especially as it’s likely switch will see more common use if it’s used regularly for type exhaustion.

[WickyNilliams]

Of course it is for your consideration. It’s just a suggestion, but one which I think corrects a bad design decision in JS and will certainly prevent bugs. I made this exact mistake today 😃

[WickyNilliams]

I just realised I missed an important condition:

1. all non-empty cases must have a break or a return

Would this be considered?

It is almost always a bug to not have a return/break in cases with a body. eslint has this on by default in its recommended configuration, so people are used to tools telling them this. C# has this exact rule, so there’s precedent in other languages.