Typescript: keyof another parameter?

Question

I'm making a function that works with any object like this:

function deleteKey (obj, key) {
  // This is just for an example, but you will get what kind of typing needed.
  delete obj[key];
}

How can I give typing in Typscript correctly? Is there a good way to use keyof a parameter like this?

function deleteKey (obj: object, key: keyof obj) {
  // This is just for an example, but you will get what kind of typing needed.
  delete obj[key];
}

Answer 1

Something like this should do the trick:

function deleteKey<T, K extends keyof T>(obj: T, key: K): Omit<T, K> {
    delete obj[key];
    return obj;
}

interface Foo {
    a: string;
    b: number;
    c: boolean;
}

const foo: Foo = { a: 'test', b: 12, c: true };
const foo_minus_a = deleteKey(foo, 'a');
const foo_minus_b = deleteKey(foo, 'b');
const foo_minus_c = deleteKey(foo, 'c');