How do ES6 Classes work in JavaScript?

class Person {
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }

  greet() {
    return `Hello, I'm ${this.name}`;
  }

  get birthYear() {
    return new Date().getFullYear() - this.age;
  }

  set birthYear(year) {
    this.age = new Date().getFullYear() - year;
  }
}

const john = new Person('John', 30);
john.greet(); // "Hello, I'm John"

class Employee extends Person {
  constructor(name, age, position) {
    super(name, age); // Call parent constructor
    this.position = position;
  }

  greet() {
    return `${super.greet()}, I'm a ${this.position}`;
  }
}

const jane = new Employee('Jane', 25, 'Developer');
jane.greet(); // "Hello, I'm Jane, I'm a Developer"

class MathUtils {
  static PI = 3.14159;

  static add(a, b) {
    return a + b;
  }
}

MathUtils.PI; // 3.14159
MathUtils.add(1, 2); // 3

class BankAccount {
  #balance = 0; // Private field

  deposit(amount) {
    this.#balance += amount;
  }

  getBalance() {
    return this.#balance;
  }
}