JS Practice — Built-in Objects

Utility Types — keyof Operator

📖 Usage Example

interface User { name: string; age: number }
type UserKey = keyof User   // → 'name' | 'age'
function getField(u: User, k: UserKey) { return u[k] }

keyof produces a union of an object type's property names, enabling type-safe property access.

The keyof Operator

keyof T produces a union of all property names of T.

Challenge: Implement getKeys<T extends object>(obj: T): (keyof T)[] returning all own keys.

getKeys({ a: 1, b: 2, c: 3 })  // → ['a', 'b', 'c']

💡 Hints (1)