Accessing "unknown keys" and their values from refine() without passthrough()

[Aaronius]

I have an object like so:

{
  a: "foo",
  b: "foo"
}

which I'm validating using a schema like this:

z.object({
  a: z.string()
}).refine((input) => {
  // I need to reference b here
});

I can access b if I call passthrough() before refine(), like this:

z.object({
  a: z.string()
})
.passthrough()
.refine((input) => {
  // I need to reference b here
});

I don't want b to actually be passed through though. Is there a way I can access b in refine without having to call passthrough?

[scotttrinh]

I would suggest adding the b schema and using refine to do your check and then transform to only return a.

[Aaronius]

That's workable. Thanks. It seems like a better solution would be to allow this to be configured through RefineParams. I think I'll open an issue for that.