Just have default throw an error? Then, if you add a value to the string union (hopefully) your tests will highlight it isnt handled.
Equally, for such a simple switch, surely a map is better?
But i rarely find myself using switches.
I find ifs with early returns cleaner. Allows for variable creation during execution (which my tslint complains about)
Generally, I would recommend against throwing in the default case, since it will actually reduce your type safety (exceptions bypass all your other types). But I learned that with another clever trick this can be avoided, giving both runtime and compile time safety: https://exploringjs.com/tackling-ts/ch_enums.html#exhaustiveness-checks
I really appreciate compile errors in this scenario. In Rust the compiler will freak out when there are missing enum variants in a match. Tests are great, but compiler errors don't rely on exhaustive and properly written tests.
I haven't had a chance to try it myself yet. I saw someone give a recommendation for ts-pattern which provides functions for pattern matching with optional exhaustion.
There is support for this in Effect as another implementation.