Objects

const person = {
  name: "Alice",
  age: 30,
  city: "New York",
  isEmployed: true
};

console.log(person.name);     // => "Alice"
console.log(person.age);      // => 30

// Dot notation (preferred when property name is known)
console.log(person.name);     // => "Alice"

// Bracket notation (needed for dynamic or invalid identifiers)
console.log(person["name"]);  // => "Alice"

// Dynamic property access
const key = "city";
console.log(person[key]);     // => "New York"

// Bracket notation allows characters that dot notation doesn't
const obj = {
  "first name": "Alice",     // Space in property name — must use quotes
  "123start": "value"        // Starts with a digit — must use quotes
};
console.log(obj["first name"]);  // => "Alice"
// console.log(obj.first name)   // ❌ SyntaxError

const user = { name: "Alice" };

// Add new property
user.age = 30;
user["email"] = "alice@example.com";

// Update existing
user.name = "Bob";

console.log(user);
// => { name: "Bob", age: 30, email: "alice@example.com" }

const calculator = {
  value: 0,

  add(n) {
    this.value += n;     // `this` refers to the calculator object
    return this;         // Return `this` for method chaining
  },

  subtract(n) {
    this.value -= n;
    return this;
  },

  getResult() {
    return this.value;
  }
};

calculator.add(5).subtract(2).add(10);
console.log(calculator.getResult());  // => 13

const key = "dynamicKey";
const obj = {
  [key]: "dynamic value",
  [`${key}2`]: "also dynamic",
  [`user_${Math.random()}`]: "random key"
};

console.log(obj.dynamicKey);    // => "dynamic value"
console.log(obj.dynamicKey2);   // => "also dynamic"

const name = "Alice";
const age = 30;

// Old way
const person1 = { name: name, age: age };

// Shorthand (ES6)
const person2 = { name, age };

console.log(person2);  // => { name: "Alice", age: 30 }

const user = {
  name: "Alice",
  greet() {
    console.log(`Hello, I'm ${this.name}`);
  }
};

user.greet();  // => "Hello, I'm Alice"

// Arrow functions do NOT have their own `this` — they inherit from parent scope
const user2 = {
  name: "Bob",
  greet: () => {
    console.log(`Hello, I'm ${this.name}`);  // `this` is NOT user2! (window/undefined)
  }
};

user2.greet();  // => "Hello, I'm undefined"  (or "Hello, I'm " in browser)

const person = { name: "Alice", age: 30, city: "New York" };

// Basic destructuring
const { name, age } = person;
console.log(name);  // => "Alice"
console.log(age);   // => 30

// Rename variables
const { name: personName, city: location } = person;
console.log(personName);  // => "Alice"
console.log(location);    // => "New York"

// Default values
const { country = "Unknown" } = person;
console.log(country);  // => "Unknown"

// Nested destructuring
const user = {
  id: 1,
  profile: {
    displayName: "Alice",
    avatar: "alice.jpg"
  }
};
const { profile: { displayName } } = user;
console.log(displayName);  // => "Alice"

// Copy an object
const original = { a: 1, b: 2 };
const copy = { ...original };
console.log(copy);  // => { a: 1, b: 2 }

// Merge objects (later properties override earlier ones)
const defaults = { theme: "light", showSidebar: true };
const userPrefs = { theme: "dark" };
const config = { ...defaults, ...userPrefs };
console.log(config);  // => { theme: "dark", showSidebar: true }

// Add new properties while copying
const base = { name: "Alice" };
const extended = { ...base, age: 30, role: "admin" };
console.log(extended);  // => { name: "Alice", age: 30, role: "admin" }

const user = { name: "Alice", age: 30, city: "New York" };

console.log(Object.keys(user));     // => ["name", "age", "city"]
console.log(Object.values(user));   // => ["Alice", 30, "New York"]
console.log(Object.entries(user));  // => [["name","Alice"], ["age",30], ["city","New York"]]

// Iterate over entries
for (const [key, value] of Object.entries(user)) {
  console.log(`${key}: ${value}`);
}
// name: Alice
// age: 30
// city: New York

const user = { name: "Alice", age: 30 };

// in operator
console.log("name" in user);   // => true
console.log("email" in user);  // => false

// hasOwnProperty
console.log(user.hasOwnProperty("name"));  // => true

// undefined check (works but can be misleading)
console.log(user.email === undefined);  // => true
// BUT: property might exist with value undefined
const obj = { x: undefined };
console.log(obj.x === undefined);  // => true (property exists!)
console.log("x" in obj);           // => true (better check)

const user = {
  name: "Alice",
  address: {
    street: "123 Main St"
    // zipCode is missing
  }
};

// Without optional chaining
console.log(user.address.zipCode);  // => undefined (ok)
// console.log(user.billing.address); // ❌ TypeError: Cannot read property 'address' of undefined

// With optional chaining
console.log(user.billing?.address);  // => undefined (safe)
console.log(user.billing?.address?.street);  // => undefined (safe)

// 1. Create a book object with title, author, year, and a method getSummary()
// 2. Use destructuring to extract title and author
// 3. Use spread to merge it with a rating object { rating: 4.5 }
// 4. Use Object.entries() to log all key-value pairs
// 5. Use optional chaining to access a nested property safely

const book = {
  title: "JavaScript Fundamentals",
  author: "Jane Doe",
  year: 2026,
  getSummary() {
    return `${this.title} by ${this.author} (${this.year})`;
  }
};

const { title, author } = book;
const fullBook = { ...book, rating: 4.5 };
console.log(fullBook.getSummary());  // => "JavaScript Fundamentals by Jane Doe (2026)"