JavaScript Objects: Creating, Reading, Updating, and Managing Properties

const user = {
  name: "Priya", // string  age: 22,                   // number  isMember: true,            // boolean  skills: ["HTML", "CSS"],   // array — objects hold anything!  address: {
  // nested object ✅    city: "Mumbai",    pin: 400001
}
};

const cart = {
};
// start emptycart.item = "Keyboard";          // fill it up as you gocart.price = 1299;

class User {
  constructor(name) {
    this.name = name;
  }
}const user1 = new User("Amit");
// one blueprint, many objects

const proto = {
  greet() {
    return "Hi!";
  }
};
const obj = Object.create(proto);
// creates with a custom prototype

console.log(user.name);
// "Priya"console.log(user.address.city);   // "Mumbai" — chain through nesting

console.log(user["name"]);
// "Priya" — same result

// ① Dynamic keys — the property name lives in a variable:
const key = "age";
console.log(user[key]);
// 22 ✅ — dots can't do this!
// ② Keys with spaces or special characters:
const prefs = {
  "theme color": "dark"
};
console.log(prefs["theme color"]);
// ✅ brackets required
// prefs.theme color               // ❌ syntax error!
// ③ Keys built on the fly:
const id = 42;
const responses = {
  "user-42": "ok"
};
console.log(responses["user-" + id]);
// "ok" ✅

console.log(user.phone);
// undefined — no error, just undefined 🤫
console.log(user.phone.number);
// ❌ TypeError! — reading OF undefined
// ✅ Safe version (optional chaining — Lesson 6):
console.log(user?.phone?.number);
// undefined — no crash ✅

const product = {
  title: "Mouse", price: 599
};
// Update existing:
product.price = 499;
// ✏️ updated
// Add brand new:
product.stock = 25;
// ➕ created on the spot!
product["in stock"] = true;
// brackets work too
console.log(product);
// { title: "Mouse", price: 499, stock: 25, "in stock": true }

const user = {
  name: "Priya", tempToken: "abc123", age: 22
};
delete user.tempToken;
// 🗑️ gone
console.log(user.tempToken);
// undefined
console.log(user);
// { name: "Priya", age: 22 }

const {
  tempToken, ...cleanUser
} = user;
// pull out tempToken, keep the rest
console.log(cleanUser);
// { name: "Priya", age: 22 } ✅
// original untouched — the React/Redux way!

const user = {
  name: "Priya", age: 22
};
console.log("name" in user);
// true ✅
console.log("phone" in user);
// false
// The gotcha: a key can exist with an undefined value!
const data = {
  result: undefined
};
console.log("result" in data);
// true — key EXISTS
console.log(data.result);
// undefined — value is empty
console.log(data.hasOwnProperty("result"));
// true — the classic checker ✅

const product = {
  title: "Keyboard", price: 1299, stock: 15
};
Object.keys(product);
// ["title", "price", "stock"] — the keys
Object.values(product);
// ["Keyboard", 1299, 15] — the values
Object.entries(product);
// [["title","Keyboard"], ["price",1299], …] — pairs

// Loop the keys:
Object.keys(product).forEach(key => {
  console.log(`${key}: ${product[key]}`);
  // brackets — dynamic keys! 🎯
});
// Loop the pairs directly (the cleanest way):
Object.entries(product).forEach(([key, value]) => {
  console.log(`${key} → ${value}`);
});
// Real-world: find expensive items in a price list:
const prices = {
  keyboard: 1299, mouse: 599, cable: 199
};
Object.entries(prices) .filter(([item, price]) => price > 500) // filter pairs!
.forEach(([item, price]) => console.log(`💰 ${item}: ₹${price}`));
// 💰 keyboard: ₹1299
// 💰 mouse: ₹599

const defaults = {
  theme: "light", fontSize: 14
};
const userPrefs = {
  fontSize: 18
};
const settings = {
  ...defaults, ...userPrefs
};
console.log(settings);
// { theme: "light", fontSize: 18 } — last wins! ✅
// True copy:
const copy = {
  ...defaults
};
// The older way you'll see in legacy code:
const merged = Object.assign( {
}, defaults, userPrefs);
// same result

const config = Object.freeze( {
  appName: "MyShop", version: "2.0"
});
config.version = "3.0";
// silently ignored (TypeError in strict mode!)
delete config.appName;
// also blocked
console.log(config.version);
// "2.0" — frozen solid ❄️

✨ New product: monitor📦 Restocked mouse: +10Mouse price: 599Cable price: not found 🔍🗑️ keyboard discontinued📊 INVENTORY REPORTmouse: ₹599 — 10 in stock ✅monitor: ₹8999 — 5 in stock ✅Total products: 2