Typescript: How to map string type to generic with many different subtypes

Question

I am trying to create a typed interface on top of local storage where I can set/get from local storage in a typed way using only a string key. I want to have a mapping of the string types to generics that allows me to have custom serialization/deserialization.

The issue I am running into is that Typescript doesn't seem to be able to properly infer the types when I use a mapping object to go from the string type to the object generic. If anyone has some good advice on the best way to go about this, that would be amazing! ❤️

I have an example below that might explain my situation better:

type LocalStorageKey = "bool_test" | "num_test";

type LocalStorageKeyInfo<T> = {
  key: LocalStorageKey;
  getDefault(): T;
  serialize(val: T): string;
  deserialize(lsVal: string | null, defaultVal: T): T;
};

const BooleanSerializer = (val: boolean) => String(val);
const BooleanDeserializer = (lsVal: string | null, defaultVal: boolean) => {
  if (lsVal === null) {
    return defaultVal;
  } else {
    return lsVal === "true";
  }
};

const NumberSerializer = (val: number) => String(val);
const NumberDeserializer = (lsVal: string | null, defaultVal: number) => {
  if (lsVal === null) {
    return defaultVal;
  } else {
    return Number(lsVal);
  }
};

export const BoolTestKeyInfo: LocalStorageKeyInfo<boolean> = {
  key: "bool_test",
  getDefault: () => false,
  serialize: BooleanSerializer,
  deserialize: BooleanDeserializer,
};

export const NumTestKeyInfo: LocalStorageKeyInfo<number> = {
  key: "num_test",
  getDefault: () => 0,
  serialize: NumberSerializer,
  deserialize: NumberDeserializer,
};

const keyInfoMapping = {
  bool_test: BoolTestKeyInfo,
  num_test: NumTestKeyInfo,
};

export function getKeyVal(key: LocalStorageKey) {
  const keyInfo = keyInfoMapping[key];
  try {
    return keyInfo.deserialize(
      window.localStorage.getItem(keyInfo.key),
      // This line is the issue because deserialize's second arg is infered as never
      keyInfo.getDefault()
    );
  } catch (e) {
    return keyInfo.getDefault();
  }
}

// I want x to be a boolean here
const x = getKeyVal("bool_test");