const obj = {
  name: 'ellie',
};
obj.name;    *// ellie*
obj['name']; *// ellie*

type Animal = {
  name: string;
  age: number;
  gender: 'male' | 'female';
};
 
*// #1*
type Name = Animal['name'];
const text: Name = 'hello';

*// #2*
type Gender = Animal['gender']; *// 'male' | 'female'*

*// #3*
type Keys = keyof Animal;       *// 'name' | 'age' | 'gender'*
const key: Keys = 'gender';

// #4
type Person = {
  name: string;
  gender: Animal['gender'];
}
const person: Person = {
  name: 'ellie',
  gender: 'female',
}