How to use Typescript Generics in modifier functions

Question

I am looking for a way to correctly strong type a below case, I suspect i need to use Typescript Generics in this situation.

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

const person: Person = {
  name: "John",
  age: 30,
};

const alterPerson = (key: keyof Person, val) => {
  person[key] = val;
}

My intention is that function 'alterPerson' is aware it can only take Person keys as its first argument and then, once it has taken a key i want the function to know what type of value can be assigned to that key.

Can you show me how this could be done. Thank you!

Answer 1

alterPerson is still directly coupled to the person variable. To make this truly reusable with generics, you'd need to also pass that variable as a function parameter.

const alterObject = <T>(object: T, key: keyof T, val: T[keyof T]) => {
  object[key] = val;
}