text: //ES6 Classes
  class Person {
      constructor(firstName, lastName, dob) {
          this.firstName = firstName;
          this.lastName = lastName;
          this.birthday = new Date(dob);
      }
  
      greeting() {
          return `Hello there ${this.firstName} ${this.lastName}`;
      }
      calculateAge(){
          const diff = Date.now() - this.birthday.getTime();
          const ageDate = new Date(diff);
          return Math.abs(ageDate.getUTCFullYear() - 1970);
      }
      getsMarried(newLastName) {
          this.lastName = newLastName;
      }
      static addNumbers(x,y){
          return x + y;
      }
  }
  
  const mary = new Person('Mary', 'Williams', '11-13-1980');
  
  mary.getsMarried('Thompson');
  
  console.log(mary);
  
  //sub classes
  class Person {
      constructor(firstName, lastName,) {
          this.firstName = firstName;
          this.lastName = lastName;
      }
      greeting() {
          return `Hello there ${this.firstName} ${this.lastName}`;
      }
  }
  
  class Customer extends Person {
      constructor(firstName, lastName, phone, membership) {
          super(firstName, lastName);
  
          this.phone = phone;
          this.membership = membership;
      }
      static getMembershipCost() {
          return 500
      }
  
  }
  
  const john = new Customer('John', 'Doe', '555-555-5555', 'full');
  
  console.log(john);