const values

[mfulton26]

I want to be able to validate that a value is one of several specific values and then get a union type returned

e.g.

ow.string.oneOf(["on", "off"] as const)

The type would be StringPredicate<"on" | "off"> rather than simply StringPredicate or some subclass of Predicate<T>.

A different solution that might work would be to use ow.any(…) so that union types can be defined for more than just strings:

ow.any(ow.const("on" as const), ow.const("off" as const))

[sindresorhus]

I think both would be useful, but I haven't looked into whether it's possible.