Amend an existing Type.Object

[wyozi]

Hey, would it be possible to amend an existing type object in a stable way?

I mean something like

const first = Type.Object({
  x: Type.Number(),
  y: Type.Number(),
});
const second = Type.Amend(first, {
  z: Type.Number(),
})

// second is equal to 
const T = Type.Object({
  x: Type.Number(),
  y: Type.Number(),
  z: Type.Number(),
});

Seems like a bit of a weird usecase, but it's for a library concept I'm prototyping.

[sinclairzx81]

@wyozi Hi, Does this work?

TypeScript Link Here

import { Type, Static, TObject, TProperties } from '@sinclair/typebox'

export const Amend = <T extends TObject, P extends TProperties>(schema: T, properties: P) => 
  Type.Composite([schema, Type.Object(properties)])

const first = Type.Object({
  x: Type.Number(),
  y: Type.Number()
})

const second = Amend(first, {
  z: Type.Number()
})

type T = Static<typeof second>

[wyozi]

@sinclairzx81 thanks! This works very well for additive partial schemas! :)

This is already enough for most cases, but just wondering would there be a way to do deletions/replacements as well?

Namely,

const third = Amend(second, {
  z: Type.Never()
}) // -> { x: number; y: number; }

const third = Amend(second, {
  z: Type.String
}) // -> { x: number; y: number; z: string }

[sinclairzx81]

@wyozi Heya. TypeBox is built to mirror TypeScript and supports most of the built in utility types. You can compose those additional types in the following way.

TypeScript Link Here

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

export const Amend = <T extends TObject, P extends TProperties>(schema: T, properties: P) => 
  Type.Composite([schema, Type.Object(properties)])

const first = Type.Object({
  x: Type.Number(),
  y: Type.Number()
})

const second = Amend(first, {
  z: Type.Number()
})

const third = Type.Omit(second, ['z'])           // delete z: number

const fourth = Amend(third, {                    // add z: string
  z: Type.String()
})

Have a read over https://www.typescriptlang.org/docs/handbook/utility-types.html for a bit more information on TypeScript utility types (specifically Pick and Omit)