Class Inheritance & Abstract Classes

Inheritance

class Employee extends Person {
  private employeeId: string;
  constructor(name: string, ssn: string, birthYear: number, employeeId: string) {
    super(name, ssn, birthYear);
    this.employeeId = employeeId;
  }
  getId() { return this.employeeId; }
}

Abstract Classes

abstract class Shape {
  abstract area(): number; // must be implemented by subclasses
}

class Circle extends Shape {
  constructor(public radius: number) { super(); }
  area() { return Math.PI * this.radius ** 2; }
}

instanceof Checks

function isShape(x: any): x is Shape {
  return x instanceof Shape;
}