Ensuring adherence to existing TypeScript interface

[sdc395]

Hi all

I've tried to find the answer to this question myself, but no luck. Is there a utility type in TypeBox that will let me check a schema's adherence to an exiting type. Something like Superstruct's Describe type. To illustrate...

interface User {
    name: string;
    age: number;
}

const user: Describe<User> = Type.Object({
    name: Type.String(),
    age: Type.Number(),
});

Thanks

[sinclairzx81]

@sdc395 Hi,

Sorry for the delay in reply on this one (I must have missed this question). TypeBox doesn't have a Describe<T> utility type built in, but it does have types to express each schematic. By convention, TypeBox types are prefixed with T, so you can enforce structures in the following way.

import { Type, TObject, TString, TNumber } from '@sinclair/typebox'

const user: TObject<{
   name: TString,
   age: TNumber
}> = Type.Object({
    name: Type.String(),
    age: Type.Number(),
})

Additionally, it's possible to implement Describe<T> through conditional mapping. The following is one way you can achieve this.

TypeScript Link Here

import { TObject, TString, TNumber, TBoolean, TUnknown } from '@sinclair/typebox'

export type Describe<T> = 
  T extends Record<any, unknown> ? TObject<{ [K in keyof T]: Describe<T[K]> }> :
  T extends string ? TString :
  T extends number ? TNumber :
  T extends boolean ? TBoolean :
  TUnknown

type TUser = Describe<{ // hover TUser
  name: string
  age: number
}>

Conditional mapping arrays, tuples, unions, intersections and other constructs is an exercise ill leave for you.

Hope this helps!
S