Return property from object with correct type using generic typing in typescript

Question

I have, many times, tried to implement generic functions that extract properties from an object. The code underneath in Typescript it returns string | number, though I wanted it to know that it will return a string or a number specifically. In plain JS I would know that the code underneath would return a string and react accordingly, so I hope any light to how this can be solved in Typescript can be shed.

interface Person {
  name: string;
  age: number;
}

const getPropertyByKey = (
  person: Person
) => (
  key: keyof Person
) => person[key];

const person = {
  name: 'Thomas',
  age: 32
};

const property = (person)('name'); // Should realise it is a string

Answer 1

Make the partial function generic and it will be able to infer the type of the return value based on the specific string value of key.

interface Person {
  name: string;
  age: number;
}

const getPropertyByKey = (
  person: Person
) => <K extends keyof Person>(
  key: K
) => person[key];

const person = {
  name: 'Thomas',
  age: 32
};

const property = getPropertyByKey(person)('name');

Playground Link