How to cast string to number?

I have something like this:

const params = z.object({
  id: z.number()
})

This fails immediately since id is a query string param and so is a string. Then I tried:

const params = z.object({
  id: z.transformer(z.string(), z.number(), x => Number(x))
})

But the compiler yells:

Type 'ZodObject<{ id: ZodTransformer<ZodString, ZodNumber>; }, "passthrough", ZodTypeAny, { id: number; }, { id: string; }>' is not assignable to type 'ZodType<{ id: number; }, ZodTypeDef, { id: number; }>'.
  The types of '_input.id' are incompatible between these types.
    Type 'string' is not assignable to type 'number'

What am I doing wrong?

[colinhacks]

There’s a lot to unpack here.

1. ZodSchema is an alias for ZodType, they’re interchangable.
2. Since the introduction of transformers in v2, ZodType is a generic class with three generic parameters: ZodType<Output, Def, Input>. For transformers Input and Output are different, for all other schemas they’re the same.
3. For the sake of backwards compatibility, if you leave out Input from the generic definition (like you do with ZodType<P>) then the Input defaults to Output. You can see this here:

Anyway, the solution is to fully type the ZodTypes in your interface. Without your full code I can’t test it myself. This should work:

interface RouteDefinition<I, O, P> {
  path: string
  method?: HttpMethod
  validate?: {
    input?: ZodType<I, any, any>
    output?: ZodType<O, any, any>
    params?: ZodType<P, any, any>
  }
  resolve(ctx: Context<I, P>): Promise<Response<O>>
}

[brielov]

@MFogleman Hi there, I’m not using Hapi, I was just making a proof of concept. The idea was to build a very simple type-safe http server from scratch. You can check it out here. I know the code sucks but the idea was to define a route specifying the body, params and return body types and return the appropiate http status code if any of the validation fails. I manage to make it work by doing ZodType<T, any, any> but I’ll check out what you specified in your comment.