Support for custom validation

[pierreis]

Is there any plan to support custom validation?
It could be of the form: z.string().validate(someValidationFunction).

That would be a great help to build advanced schemas.

This could also take the form of custom types, but for now, z.ZodType / z.ZodTypeDef not being exposed as part of the API make it a hack IMO.

[pierreis]

One way to perform this would be to add in a method in ZodType of the form:

validate(fn: Predicate<Type>, msg: ErrorMsg<Type>) => ZodType<Type, Def>

With:

type ErrorMsg<T> = string | ((obj: T) => string)
type Predicate<T> = (t: Type) => boolean

Predicates could be passed to the parser, and checked after type validation.

This would be a strong base to implement Joi-like validation methods, while remaining compatible with the various libraries offering predicate-base data validation for the time being. It would ease the implementation of custom types:

const uuid = z.string().validate(isUUID, (v: string) => `${v} is not a UUID`)

This relates to #3.

[colinhacks]

This is doable. I'm working on a big rewrite currently (probably gonna be Zoe 2) and I'll include this in that release.

[pierreis]

Sounds great. Do you need help in doing so?

[colinhacks]

The codebase is currently not fit for human eyes...

In the meantime I just implemented .refine which will let you accomplish this. Documented here. Give it a try and let me know if you have any issues. 👍

[jjhiggz]

I don't see it in the documentation on this for some reason, but I'm wondering if this got added somewhere.

I was poking around and found a .custom on the z object, and got it to work by doing the following.

const isValidPhoneNumber = (phonenumber: string) => phonenumber.length > 3

const SignupValidation = z.object({
  email: z.string().email(),
  cell: z
   // Input 1 seems to be your validator function, which should return true or false depending on the input
   // Input 2 seems to be how you control what messages show up
    .custom(isValidPhoneNumber, { message: "Not a valid phone number" })
    .transform(parseInt),
})

Obviously that's not a real phone validation, but the logic works for implementing a custom validation.
You can ignore the transform key, and also the email in the validation. I just like providing a little extra context with these answers.

Update

I think this approach using refine is probably better because then zod can first verify the type, then refine that type. As a side bonus you can use the input value to make your error message which seems cool

    const isPhoneNumber = (ph: string) => ph.length > 4;
    const phoneNumberSchema = z.string().refine(isPhoneNumber, (val) => ({
      message: `${val} is not a valid phone number`,
    }));

It also means you can infer the schema type which you can not do with z.custom

[slaesh]

so, is there something to add a "custom" validator which would then infer a "custom type" aswell?

imagine using zod in combination with prisma, having a JSONB field.. which should get a custom validation and should be properly typed for the app. :)

[slaesh]

probably found it: z.custom<{ arg: string }>