TypeScript introduces a flexible generic type, Optional<T, Props>, allowing customized props for a specific

Question

TypeScript introduces a flexible generic type, Optional<T, Props>, allowing customized props for a specific

In my attempt to develop a type called Optional<T, TProps>, where T represents the initial type and TProps is a union type of properties that need to be optional.

As an illustration:

type A = Optional<{a: string, b: string}, 'a'>

const a: A = {b: 'foo'} // No Error

I had anticipated this approach to work flawlessly but unfortunately it's not functioning as expected:


type Optional<T extends object, TProps extends keyof T> =
  {[TKey in keyof T]: TKey extends TProps ? T[TKey] | never : T[TKey]}

typescript

Answer 1

Answer №1

Based on the code provided, it appears that combining the Exclude and Pick solutions is necessary.

I have experimented with them and discovered that the following solution seems to work:

type OptionalType<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>> & Partial<Pick<T, K>>

In the example below, an error will be displayed if a field is incorrectly added to b, but it will not highlight if the optional parameter is removed:

interface ExampleInterface {
  a: number
  b: number
  g: string,
  f: boolean
}

const objA: ExampleInterface = {a: 1, b: 2, g: 'sdf', f: true}

const objB: OptionalType<ExampleInterface, 'g'> = {a: 5, b: 1, f: true}

Answer 2

Based on the code provided, it appears that combining the Exclude and Pick solutions is necessary.

I have experimented with them and discovered that the following solution seems to work:

type OptionalType<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>> & Partial<Pick<T, K>>

In the example below, an error will be displayed if a field is incorrectly added to b, but it will not highlight if the optional parameter is removed:

interface ExampleInterface {
  a: number
  b: number
  g: string,
  f: boolean
}

const objA: ExampleInterface = {a: 1, b: 2, g: 'sdf', f: true}

const objB: OptionalType<ExampleInterface, 'g'> = {a: 5, b: 1, f: true}

TypeScript introduces a flexible generic type, Optional<T, Props>, allowing customized props for a specific

Answer №1

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