Object-Oriented JavaScript: Objects, Classes, Methods, and Design Concepts

class BankAccount {
  constructor(owner, balance = 0) {
    // = 0 is a DEFAULT value!    this.owner = owner;    this.balance = balance;  }
    deposit(amount) {
      this.balance += amount;
      console.log(`💰 +₹${amount} → Balance: ₹${this.balance}`);
    } withdraw(amount) {
      if (amount > this.balance) {
        console.log(`❌ ${this.owner}: insufficient funds!`);
        return;
      } this.balance -= amount;
      console.log(`💸 -₹${amount} → Balance: ₹${this.balance}`);
    }
  }const account = new BankAccount("Priya", 1000);
  account.deposit(500);
  // 💰 +₹500 → Balance: ₹1500account.withdraw(2000);   // ❌ Priya: insufficient funds!account.withdraw(300);    // 💸 -₹300 → Balance: ₹1200

class Wallet {
  #balance = 0;
  // 🔒 truly private — invisible outside!
  addMoney(amount) {
    if (amount > 0) {
      this.#balance += amount;
    }
  } getBalance() {
    return `₹${this.#balance}`;
    // read through a controlled door
  }
}const wallet = new Wallet();
wallet.addMoney(500);
console.log(wallet.getBalance());
// "₹500"
console.log(wallet.#balance);
// ❌ SyntaxError — private!

class Vehicle {
  constructor(brand) {
    this.brand = brand;
  } start() {
    console.log(`${this.brand} engine started 🔑`);
  }
}// Car INHERITS everything from Vehicle:
class Car extends Vehicle {
  honk() {
    console.log(`${this.brand} says: Beep beep! 📢`);
  }
}const myCar = new Car("Toyota");
myCar.start();
// "Toyota engine started 🔑" — inherited from Vehicle!
myCar.honk();
// "Toyota says: Beep beep! 📢" — Car's own method

class ElectricCar extends Vehicle {
  constructor(brand, batterySize) {
    super(brand);
    // ☎️ call the parent's constructor first!
    this.batterySize = batterySize;
  } charge() {
    console.log(`${this.brand} charging ${this.batterySize}kWh 🔋`);
  }
}const tesla = new ElectricCar("Tesla", 75);
tesla.start();
// "Tesla engine started 🔑" (inherited)
tesla.charge();
// "Tesla charging 75kWh 🔋" (own)

class Animal {
  speak() {
    console.log("Some generic animal sound…");
  }
}class Dog extends Animal {
  speak() {
    console.log("Woof! 🐕");
  }
}class Cat extends Animal {
  speak() {
    console.log("Meow! 🐈");
  }
}const animals =[new Dog(), new Cat(), new Animal()];
for (let animal of animals) {
  animal.speak();
  // same command — each responds its OWN way!
}// Woof! 🐕
// Meow! 🐈
// Some generic animal sound…

class CoffeeMachine {
  brew() {
    this.#heatWater();
    // complex steps…
    this.#grindBeans();
    // …hidden inside
    this.#pour();
    console.log("☕ Your coffee is ready!");
  } #heatWater() {
    console.log("  (heating to 94°C…)");
  } #grindBeans() {
    console.log("  (grinding beans…)");
  } #pour() {
    console.log("  (pouring…)");
  }
}const machine = new CoffeeMachine();
machine.brew();
// one simple button — complexity hidden ✅