.ts

// It is the worht mentioning that Putting I+your interface name is best practice
// we define our Date shape object
interface IDate {
  year:number;
  month:number;
  day:number;
}

interface IPerson{
  name:string;
  gender:string;
  birthday:Date; // here we can easily use our defined interface
}

// now we have all the fields Person and Student
interface IStudent extends IPerson{
  department:string;
  courseSection:number;
}