Keyof typescript

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

type K1 = keyof Person; // "name" | "age" | "location"
type K2 = keyof Person[];  // "length" | "push" | "pop" | "concat" | ...
type K3 = keyof { [x: string]: Person };  // string

function getProperty<T, K extends keyof T>(obj: T, key: K) {
    return obj[key];  // Inferred type is T[K]
}

function getKey<T, K extends keyof T>(obj: T, key: K) {
    const x = obj[key];
    return key;  // Inferred type is T[K]
}

const nameof = <T>(name: keyof T) => name;

let x: Person = { name: "hello!", age: 20, location: "syd" };
console.log(getProperty(x, "name"));
console.log(getKey(x, "yo"));
console.log(nameof<Person>("name"));