Converting unknown attributes into choices that can be omitted

Question

Converting unknown attributes into choices that can be omitted

I am currently working on creating a mapped type that will turn certain properties into optional ones if they can be undefined.

To elaborate, my starting point is a type structured like this:

interface Input {
  foo: string;
  bar: string | undefined;
  baz: number | undefined;
}

The objective is to use a Mapped Type to convert it into the desired structure below:

interface Output {
  foo: string;
  bar?: string;
  baz?: number;
}

All the examples I have come across so far demonstrate making all properties optional, but that's not exactly what I need in this case.

typescript typescript-generics

Answer 1

Answer №1

Below is a potential solution (utilizing TS 4.1):

interface Input {
    foo: string;
    bar: string | undefined;
    baz: number | undefined;
}

type UndefinedToOptional = { 
  [K in keyof Input as undefined extends Input[K] ? K : never]?: Input[K] 
}

type T1 = Omit<Input, keyof UndefinedToOptional> & UndefinedToOptional
/* 
{
    foo: string;
    bar?: string | undefined;
    baz?: number | undefined;
}
 */

Answer 2

Below is a potential solution (utilizing TS 4.1):

interface Input {
    foo: string;
    bar: string | undefined;
    baz: number | undefined;
}

type UndefinedToOptional = { 
  [K in keyof Input as undefined extends Input[K] ? K : never]?: Input[K] 
}

type T1 = Omit<Input, keyof UndefinedToOptional> & UndefinedToOptional
/* 
{
    foo: string;
    bar?: string | undefined;
    baz?: number | undefined;
}
 */

Answer 3

Answer №2

interface InputData {
  name: string;
  type: string | undefined;
  value: number | undefined;
}

// test cases
const data1: InputData = { name: '' } // error
const data2: InputData = { name: '', type: '', value: undefined } // valid

type UndefinedProperties<T> = {
  [P in keyof T]: undefined extends T[P] ? P : never
}[keyof T];

type RemoveUndefinedValues<T> = {
  [P in keyof T]: undefined extends T[P] ? NonNullable<T[P]> : never;
}

type OutputData = 
  Omit<InputData, UndefinedProperties<InputData>> // { name: string }
  & Partial<RemoveUndefinedValues<Pick<InputData, UndefinedProperties<InputData>>>; // { type: string; value: string; }

// test cases for output
const result1: OutputData = { name: '' }; // valid
const result2: OutputData = { name: '', type: '', value: undefined } // valid

TypeScript Playground

Answer 4

interface InputData {
  name: string;
  type: string | undefined;
  value: number | undefined;
}

// test cases
const data1: InputData = { name: '' } // error
const data2: InputData = { name: '', type: '', value: undefined } // valid

type UndefinedProperties<T> = {
  [P in keyof T]: undefined extends T[P] ? P : never
}[keyof T];

type RemoveUndefinedValues<T> = {
  [P in keyof T]: undefined extends T[P] ? NonNullable<T[P]> : never;
}

type OutputData = 
  Omit<InputData, UndefinedProperties<InputData>> // { name: string }
  & Partial<RemoveUndefinedValues<Pick<InputData, UndefinedProperties<InputData>>>; // { type: string; value: string; }

// test cases for output
const result1: OutputData = { name: '' }; // valid
const result2: OutputData = { name: '', type: '', value: undefined } // valid

TypeScript Playground

Converting unknown attributes into choices that can be omitted

Answer №1

Answer №2

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