A Typescript function will only return a partial if the parameter passed into it is also

Question

A Typescript function will only return a partial if the parameter passed into it is also

I have a function that takes a camelCase object and returns the same object in snake_case format.

// Let's consider these types
interface CamelData {
   exempleId: number
   myData:string
}

interface SnakeData {
   exemple_id: number
   my_data: string
}

export const camelToSnake = (
  camelData: Partial<CamelData>
): Partial<SnakeData> => {
  return {
    exemple_id: camelData.exempleId,
    my_data: camelData.myData
}

My goal is to make sure that the return type of the function is SnakeData when the input type is CamelData.

I'm looking for a solution that works like this:

export const camelToSnake = (
  camelData: Partial<CamelData>
): if (camelData is of type CamelData) {SnakeData} else {Partial<SnakeData>} => {
  return {
    exemple_id: camelData.exempleId,
    my_data: camelData.myData
}

Any suggestions or help would be greatly appreciated. Have a wonderful day!

typescript

Answer 1

Answer №1

Understanding Function Overloading:

export function convertCamelToSnake (camelData: CamelData): SnakeData;
export function convertCamelToSnake (camelData: Partial<CamelData>): Partial<SnakeData>;
export function convertCamelToSnake (camelData: Partial<CamelData>): Partial<SnakeData> {
  return {
    example_id: camelData.exampleId,
    my_data: camelData.myData
  }
}

Answer 2

Understanding Function Overloading:

export function convertCamelToSnake (camelData: CamelData): SnakeData;
export function convertCamelToSnake (camelData: Partial<CamelData>): Partial<SnakeData>;
export function convertCamelToSnake (camelData: Partial<CamelData>): Partial<SnakeData> {
  return {
    example_id: camelData.exampleId,
    my_data: camelData.myData
  }
}

Answer 3

Answer №2

To handle conversions between CamelCase and snake_case, you can utilize a generic type for the input where if it extends CamelData, the return type will be SnakeData. Otherwise, partials can be used:

// Let's consider these interface types
interface CamelData {
   exempleId: number
   myData: string
}

interface SnakeData {
   example_id: number
   my_data: string
}
// Specifying the exported call signature separately helps to simplify typechecking inside the function
// Using one call signature is possible, but convincing TypeScript that the data fits the type `T extends CamelData ? SnakeData : Partial<SnakeData>` without typecasts is challenging.
export function camelToSnake<T extends Partial<CamelData>>(
  camelData: T
): T extends CamelData ? SnakeData : Partial<SnakeData>
export function camelToSnake(
  camelData: Partial<CamelData>
): Partial<SnakeData>{
  return {
    exemple_id: camelData.exempleId,
    my_data: camelData.myData
    }
}

const x = camelToSnake({exempleId:1})
//   ^? const x: Partial<SnakeData>
const y = camelToSnake({exempleId:2, myData: "hi"})
//   ^? const y: SnakeData

playground link

For simplicity in typechecking, I have utilized a single overload to avoid complex checks within the function for conditional types. If needed with arrow notation, it would be the only viable option:

const camelToSnake = <T extends Partial<CamelData>>(
    camelData: T
):T extends CamelData ? SnakeData : Partial<SnakeData> => ({
    exemple_id: camelData.exempleId,
    my_data: camelData.myData
} as T extends CamelData ? SnakeData : Partial<SnakeData>)

Answer 4

To handle conversions between CamelCase and snake_case, you can utilize a generic type for the input where if it extends CamelData, the return type will be SnakeData. Otherwise, partials can be used:

// Let's consider these interface types
interface CamelData {
   exempleId: number
   myData: string
}

interface SnakeData {
   example_id: number
   my_data: string
}
// Specifying the exported call signature separately helps to simplify typechecking inside the function
// Using one call signature is possible, but convincing TypeScript that the data fits the type `T extends CamelData ? SnakeData : Partial<SnakeData>` without typecasts is challenging.
export function camelToSnake<T extends Partial<CamelData>>(
  camelData: T
): T extends CamelData ? SnakeData : Partial<SnakeData>
export function camelToSnake(
  camelData: Partial<CamelData>
): Partial<SnakeData>{
  return {
    exemple_id: camelData.exempleId,
    my_data: camelData.myData
    }
}

const x = camelToSnake({exempleId:1})
//   ^? const x: Partial<SnakeData>
const y = camelToSnake({exempleId:2, myData: "hi"})
//   ^? const y: SnakeData

playground link

For simplicity in typechecking, I have utilized a single overload to avoid complex checks within the function for conditional types. If needed with arrow notation, it would be the only viable option:

const camelToSnake = <T extends Partial<CamelData>>(
    camelData: T
):T extends CamelData ? SnakeData : Partial<SnakeData> => ({
    exemple_id: camelData.exempleId,
    my_data: camelData.myData
} as T extends CamelData ? SnakeData : Partial<SnakeData>)

Answer 5

Answer №3

Just thought I'd share the solution I ended up going with for my question. Big thanks to everyone who provided helpful comments and answers that led me to this decision.

interface CamelData {
   exempleId: number
   myData:string
}

interface SnakeData {
   exemple_id: number
   my_data: string
}

type SnakeDataFor<T extends Partial<CamelData>> = {
    example_id: T['exampleId'];
    my_data: T['myData'];
}

export function camelToSnake(camelData: CamelData): SnakeData;
export function camelToSnake<T extends Partial<CamelData>>(
  camelData: T
): SnakeDataFor<typeof camelData>;
export function camelToSnake<T extends Partial<CamelData>>(
  camelData: T
): SnakeDataFor<typeof camelData> {
  return {
    exemple_id: camelData.exempleId,
    my_data: camelData.myData
  }
}

This solution is a bit more advanced than what I initially requested. It returns SnakeData if the parameter is of type CamelData, otherwise it returns a custom type with the same properties as the parameter.

I'll update this post if I come across a better solution in the future.

Answer 6

Just thought I'd share the solution I ended up going with for my question. Big thanks to everyone who provided helpful comments and answers that led me to this decision.

interface CamelData {
   exempleId: number
   myData:string
}

interface SnakeData {
   exemple_id: number
   my_data: string
}

type SnakeDataFor<T extends Partial<CamelData>> = {
    example_id: T['exampleId'];
    my_data: T['myData'];
}

export function camelToSnake(camelData: CamelData): SnakeData;
export function camelToSnake<T extends Partial<CamelData>>(
  camelData: T
): SnakeDataFor<typeof camelData>;
export function camelToSnake<T extends Partial<CamelData>>(
  camelData: T
): SnakeDataFor<typeof camelData> {
  return {
    exemple_id: camelData.exempleId,
    my_data: camelData.myData
  }
}

This solution is a bit more advanced than what I initially requested. It returns SnakeData if the parameter is of type CamelData, otherwise it returns a custom type with the same properties as the parameter.

I'll update this post if I come across a better solution in the future.

A Typescript function will only return a partial if the parameter passed into it is also

Answer №1

Answer №2

Answer №3

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