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

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