How to make generics more specific?

byMR

April 18, 2024

There is a function

function createStats<K extends string[]>(arr: K): Stats<K[number]>

and when I do this for example

const testStats = createStats(["maxHealth"])

testStats is Stats<string> and I want it to be Stats<"maxHealth">

The only way I know how to fix it is to add as const. But I don’t want to write as const through out all of my code, so it isn’t really a good solution for me.

>Solution :

You can use a generic const-type parameter also known as const-modifier. Similar to a const-assertion TypeScript will try to infer the most specific type of a generic argument.

declare function createStats<const K extends readonly string[]>(
  arr: K,
): Stats<K[number]>;
createStats(["maxHealth"]);
//^? createStats<readonly ["maxHealth"]>(arr: readonly ["maxHealth"]): "maxHealth"

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