A typesafe curried getter

haskey.ts

// HasKey checks whether the given object has the specified key 'K' 
type HasKey<K extends string, V = unknown> = {[_ in K]: V};

// curried getter
const get = <K extends string, O extends HasKey<K>>(key: K) => (obj: O): O[K] => obj[key];

// the object to check
const Person = {name: 'Danny', age: '47'};

const getAge = get('age');
getAge(Person);  // ok, Person has key 'age'

const getAddress = get('address');
getAddress(Person);  // error, Person has no key 'address'