Creating nested return types: A guide to defining function return types within a Typescript class

Question

Creating nested return types: A guide to defining function return types within a Typescript class

My large classes contain functions that return complex objects which I am looking to refactor.

class BigClass {
    ...
    getReferenceInfo(word: string): { isInReferenceList:boolean, referenceLabels:string[] } {
    ...
    }
}

I am considering something like this (defining it close to the function):

class Foo {
    ...
    type ReturnObject = { isInReferenceList:boolean, referenceLabels:string[] };
    getReferenceInfo(word: string):ReturnObject   {
      ...
      }
}

However, at present Typescript restricts me to declaring interfaces/types outside of the class:

type ReturnObject = { isInReferenceList:boolean, referenceLabels:string[] };
class Foo {
    ...
    getReferenceInfo(word: string):ReturnObject   {
      ...
      }
}

Is there a way to have nested interfaces in Typescript?

typescript

Answer 1

Answer №1

In the comments, it was noted that current support for using a `class` as a namespace for type declarations is lacking. There is an open suggestion on GitHub to address this issue. If you are interested in this feature, consider visiting the GitHub page to show your support or provide insights into why it is essential.

One workaround is to utilize declaration merging as demonstrated below:

// Creating a separate namespace 😞
// Not exactly close to the method either 😢
namespace Foo {
  // Type must be exported within the namespace 😞
  export type ReturnObject = {
    isInReferenceList: boolean,
    referenceLabels: string[]
  };
}

class Foo {
  // Referring to the type with its full namespace path 😞
  getReferenceInfo(word: string): Foo.ReturnObject {
    return null!;
  }
}

Although this solution may not be ideal and does not solve the issue of bringing the type declaration closer to the method using it, it can serve as a temporary fix. Good luck!

Answer 2

In the comments, it was noted that current support for using a `class` as a namespace for type declarations is lacking. There is an open suggestion on GitHub to address this issue. If you are interested in this feature, consider visiting the GitHub page to show your support or provide insights into why it is essential.

One workaround is to utilize declaration merging as demonstrated below:

// Creating a separate namespace 😞
// Not exactly close to the method either 😢
namespace Foo {
  // Type must be exported within the namespace 😞
  export type ReturnObject = {
    isInReferenceList: boolean,
    referenceLabels: string[]
  };
}

class Foo {
  // Referring to the type with its full namespace path 😞
  getReferenceInfo(word: string): Foo.ReturnObject {
    return null!;
  }
}

Although this solution may not be ideal and does not solve the issue of bringing the type declaration closer to the method using it, it can serve as a temporary fix. Good luck!

Creating nested return types: A guide to defining function return types within a Typescript class

Answer №1

Similar questions

Thoroughly verifying API responses in RTK Query with Zod schema

How to detect changes in Angular2 forms

Creating dynamic keys to insert objects

How can I get the class name of the drop destination with react-dnd?

Get rid of the TypeScript error in the specified function

Dynamically modifying the display format of the Angular Material 2 DatePicker

Developing a loader feature in React

ways to eliminate attributes using mapped types in TypeScript

In Angular, is there a way to transform time into the format of YYYY-MM-DDThh:mm:ssTZD?

Checkbox Event Restricts Access to a Single Class Variable

Steps for removing the console warning message: "The use of enableRowSelect has been deprecated. Instead, please utilize rowSelection."

What events can cause all store states to be loaded when the page is altered?

Setting the dispatch type in Redux using Typescript

The data type '{}' cannot be assigned to the type 'WebElement'

What are the methods used in TypeScript to implement features that are not available in JavaScript, despite TypeScript ultimately being compiled to JavaScript?

Utilize the class or interface method's data type

Tips for anticipating a string that begins with a particular variable

Manipulating CSS Class Properties Using JavaScript

Unable to call an object that may be 'undefined': Utilizing a function with a return object that includes asynchronous functions as properties

Creating a specialized feature for saving form data with React Admin