The concept of type literals in Typescript provides a powerful tool for achieving function

Question

The concept of type literals in Typescript provides a powerful tool for achieving function

In TypeScript, I am aiming to create an overloaded function with named parameters. Despite the code running correctly, I encounter warnings about `init.index` potentially not existing in one of the function signatures.

The purpose of overloading is to offer mutually exclusive properties on the object based on the specifications in the documentation, which are not explicitly defined in the official library.

export function insertText(init: { text: string, index: number }): docs_v1.Schema$Request;
export function insertText(init: { text: string, segmentId?: string }): docs_v1.Schema$Request {
  return {
    insertText: {
      text: init.text,
      ...(init.index && { location: { index: init.index} }),
      ...(!init.index && { endOfSegmentLocation: { segmentId: init.segmentId } }),
    }
  }
}

I have included a TypeScript playground which showcases examples of the code and the associated errors.

Furthermore, I aim to destructure the object parameter, as detailed here.

typescript google-docs-api

Answer 1

Answer №1

It seems that your example could be enhanced by consolidating it into a single overload with a union type. When working with a union, the key is to distinguish the values effectively.

An approach could be to utilize the in typeguard:

export function combineData(input: { data: string, index: number } | { data: string, id?: string }): Result {
  return {
    data: {
      text: input.data,
      ...('index' in input && { position: { index: input.index } }),
      ...(!('index' in input) && { segment: { id: input.id } }),
    }
  }
}

Explore Example

Alternatively, if you include index in both union options, where the additional one has a type of null | undefined, you could also employ == null:

export namespace result { export interface Result {}; };

// Revised Implementation
export function combineData(input: { data: string, index: number } | { data: string, index?: undefined | null; id?: string }): result.Result {
  return {
    data: {
      text: input.data,
      ...(input.index != null && { position: { index: input.index } }),
      ...(input.index == null && { segment: { id: input.id } }),
    }
  }
}

Explore Example

Answer 2

It seems that your example could be enhanced by consolidating it into a single overload with a union type. When working with a union, the key is to distinguish the values effectively.

An approach could be to utilize the in typeguard:

export function combineData(input: { data: string, index: number } | { data: string, id?: string }): Result {
  return {
    data: {
      text: input.data,
      ...('index' in input && { position: { index: input.index } }),
      ...(!('index' in input) && { segment: { id: input.id } }),
    }
  }
}

Explore Example

Alternatively, if you include index in both union options, where the additional one has a type of null | undefined, you could also employ == null:

export namespace result { export interface Result {}; };

// Revised Implementation
export function combineData(input: { data: string, index: number } | { data: string, index?: undefined | null; id?: string }): result.Result {
  return {
    data: {
      text: input.data,
      ...(input.index != null && { position: { index: input.index } }),
      ...(input.index == null && { segment: { id: input.id } }),
    }
  }
}

Explore Example

The concept of type literals in Typescript provides a powerful tool for achieving function

Answer №1

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