CHALLENGE 2: Extend an Interface
=================================

SOLUTION:

interface Person {
  name: string;
  age: number;
}

interface Employee extends Person {
  employeeId: number;
  department: string;
}

// Create an employee
const employee: Employee = {
  name: "Alice",
  age: 30,
  employeeId: 12345,
  department: "Engineering"
};

// All of Person's properties are required too:
const anotherEmployee: Employee = {
  name: "Bob",
  age: 28,
  employeeId: 12346,
  department: "Sales"
};

EXPLANATION:
- "interface Person { ... }" — base interface with name and age
- "interface Employee extends Person { ... }" — Employee inherits from Person
- Employee MUST have: name (from Person), age (from Person), employeeId, department
- The "extends" keyword means Employee is a specialized version of Person

WHY USE INTERFACE INHERITANCE:
- DRY principle: don't repeat name and age in Employee
- Clarity: Employee IS a Person (plus more)
- Consistency: all employees have the base Person properties
- Easy to add shared properties: add to Person once, all children get it

ALTERNATIVE APPROACH (if you wanted multiple interfaces):
interface HasName {
  name: string;
}

interface HasAge {
  age: number;
}

interface Person extends HasName, HasAge {}

interface Employee extends Person {
  employeeId: number;
  department: string;
}

TESTING:
✅ Works: { name: "Charlie", age: 35, employeeId: 123, department: "HR" }
❌ Error: { name: "Charlie", employeeId: 123, department: "HR" }  (missing age from Person)
❌ Error: { name: "Charlie", age: 35, department: "HR" }  (missing employeeId)