Annotating Effectively

type Person = {
  name: string;
  age: number;
};

type Studying = {
  semester: number;
};

type Student = {
  id: string;
  age: number;
  semester: number;
};

function createPerson() {
  return { name: "Stefan", age: 39, semester: 25, id: "XPA" };
}

function printPerson(person: Person) {
  console.log(person.name, person.age);
}

function studyForAnotherSemester(student: Studying) {
  student.semester++;
}

function isLongTimeStudent(student: Student) {
  return student.age - student.semester / 2 > 30 && student.semester > 20;
}

const me = createPerson();

// All work!
printPerson(me);
studyForAnotherSemester(me);
isLongTimeStudent(me);