Narrowing empty string or false in generic misbehaves about typescript HOT 2 OPEN

TS doesn't have any type-level representation of "The truthy values of T" or "All truthy values", so at any point where we have to write down the type, the next-best thing is NonNullable<T> which is a sound but not-complete superset (it includes '' when it shouldn't) of that.

from typescript.

But it seems like it wouldn't be that troublesome to define types which extracts or excludes falsy types from a union, much like NonNullable excludes null and undefined and use those in such cases. And if T includes number, both branches would have to include number because there's no NaN type, but I think you get that part done with Extract and Exclude.

Of course I don't know what all would be involved in the change, so maybe it's a difficult ask.

from typescript.