How to Define Intersection Type with Symbol in TypeScript?

Question

How to Define Intersection Type with Symbol in TypeScript?

I'm currently working on a helper function that associates a Symbol with a value.

function setCustomSymbol<S extends symbol, T>(symbol: S, data: T, defaultValue: any = true): S & T { /*...*/ }

The issue I'm facing is trying to instruct TypeScript that the output of this function should be a value with the specified symbol property. This way, I can use it like this:

const MySymbol = Symbol();
const obj = {};

const resultWithCustomSymbol = setCustomSymbol(MySymbol, obj);

resultWithCustomSymbol[MySymbol] = true;

Is there a way to achieve this? I experimented with unique symbol but couldn't quite make it work. Thank you for your assistance!

typescript typescript-typings typescript-generics

Answer 1

Answer №1

If you possess a key of type K and wish to represent an object containing that key along with a value of type V, you can utilize the predefined Record<K, V> utility type in this manner:

function setSymbol<S extends symbol, T>(
  symbol: S, 
  on: T, 
  withValue: any = true
): Record<S, any> & T { 
    return null! // implementation here
}

(It is essential to assess your specific use case to determine if Record<S, any> suffices or if you need withValue to refine the type further). Note that Record<S, any> is equivalent to the mapped type {[K in S]: any} should you prefer to utilize that instead. Your provided example code should now function as expected:

const MySymbol = Symbol();
const value = {};
const resultWithSymbol = setSymbol(MySymbol, value);
resultWithSymbol[MySymbol] = true; // no issues
resultWithSymbol[Symbol("some other symbol")] = true; // error thrown

Hopefully, this information proves beneficial; best of luck!

Link to code

Answer 2

If you possess a key of type K and wish to represent an object containing that key along with a value of type V, you can utilize the predefined Record<K, V> utility type in this manner:

function setSymbol<S extends symbol, T>(
  symbol: S, 
  on: T, 
  withValue: any = true
): Record<S, any> & T { 
    return null! // implementation here
}

(It is essential to assess your specific use case to determine if Record<S, any> suffices or if you need withValue to refine the type further). Note that Record<S, any> is equivalent to the mapped type {[K in S]: any} should you prefer to utilize that instead. Your provided example code should now function as expected:

const MySymbol = Symbol();
const value = {};
const resultWithSymbol = setSymbol(MySymbol, value);
resultWithSymbol[MySymbol] = true; // no issues
resultWithSymbol[Symbol("some other symbol")] = true; // error thrown

Hopefully, this information proves beneficial; best of luck!

Link to code

How to Define Intersection Type with Symbol in TypeScript?

Answer №1

Similar questions

What is the best approach to implement a recursive intersection while keeping refactoring in consideration?

send mouse event to component when clicked

Navigational bar mishaps: troubleshooting the "is not a function error" in layout.tsx

One way to incorporate type annotations into your onChange and onClick functions in TypeScript when working with React is by specifying the expected

Are generic constraints leading to type inference selecting the incorrect candidate?

Changing the format of a numerical value to include commas for every 1000 increment

Navigating through a multidimensional array in Angular 2 / TypeScript, moving both upwards and downwards

How to retrieve values from multiple mat-sliders that are dynamically generated using ngFor loop

Ways to specify an unused parameter within a function

Utilizing the Double Mapping Feature in React with Typescript

What is the best approach to validating GraphQL query variables while utilizing Mock Service Worker?

What is the best way to add JSX to the DOM using React?

Retrieving the value of a selected option in Angular

Having trouble with typecasting in Angular 9 after receiving an HTTP response?

When calling UIComponent.getRouterFor, a TypeScript error is displayed indicating the unsafe return of a value typed as 'any'

Lack of Typescript 2.1 and Angular 2 type definitions with browserify

ConfirmUsername is immutable | TypeScript paired with Jest and Enzyme

Jest is having difficulty locating a module while working with Next.js, resulting in

Stop automatic scrolling when the keyboard is visible in Angular

Combining Axios with repeated promises