Creating a custom Map type in TypeScript

I am exploring the concept of defining a Map type in Typescript using generics. Essentially, I want to create something similar to:

EntityMap<U, V>, where U can only be either a string or a number

This is what I have managed to come up with so far:

export type EntityMapKey = string | number;
export type EntityMap<U, V> = { [K in EntityMapKey]: V};

However, the issue arises when this is implemented as we are able to use any type for U, as depicted below:

interface Jobs {
  list: EntityMap<Array, JobFile>
}

I am aiming to impose restrictions on using any type other than string or number for U. How can one achieve this?

Is there anything that I might be overlooking or missing out on?

angularjstypescripttypescript-generics

Answer №1

The EntityMap in your code snippet seems to have a small issue with the type parameter U not being utilized correctly. Here's a revised version for better implementation:

export type EntityMapKey = string | number;
export type EntityMap<U extends EntityMapKey, V> = { [K in U]: V};
interface Jobs {
  list: EntityMap<string, any>
}

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