Arrays & Objects Deep Dive

const fruits = ['apple', 'banana', 'cherry'];
console.log(fruits[0]);     // "apple"
console.log(fruits.length); // 3

const numbers = [1, 2, 3, 4];
const doubled = numbers.map(n => n * 2);
// [2, 4, 6, 8]

const ages = [12, 18, 25, 8, 30];
const adults = ages.filter(age => age >= 18);
// [18, 25, 30]

const users = [
  { name: 'Alice', role: 'admin' },
  { name: 'Bob', role: 'user' },
];
const admin = users.find(u => u.role === 'admin');
// { name: 'Alice', role: 'admin' }

const prices = [10, 20, 30];
const total = prices.reduce((sum, price) => sum + price, 0);
// 60

const scores = [85, 92, 78, 95];
scores.some(s => s > 90);  // true — at least one is over 90
scores.every(s => s > 70); // true — all are over 70

const products = [
  { name: 'Shirt', price: 25, inStock: true },
  { name: 'Pants', price: 50, inStock: false },
  { name: 'Hat', price: 15, inStock: true },
  { name: 'Jacket', price: 100, inStock: true },
];

const affordableInStock = products
  .filter(p => p.inStock)
  .filter(p => p.price < 50)
  .map(p => p.name);
// ['Shirt', 'Hat']

const arr = [1, 2, 3];

arr.push(4);      // add to end → [1, 2, 3, 4]
arr.pop();        // remove from end → [1, 2, 3]
arr.unshift(0);   // add to beginning → [0, 1, 2, 3]
arr.shift();      // remove from beginning → [1, 2, 3]

arr.splice(1, 1); // remove 1 item at index 1 → [1, 3]

const a = [1, 2, 3];
const b = [4, 5, 6];
const merged = [...a, ...b]; // [1, 2, 3, 4, 5, 6]

const copy = [...a]; // shallow copy

const user = {
  name: 'Alice',
  age: 28,
  email: 'alice@example.com',
  isAdmin: false,
};

console.log(user.name);      // "Alice"
console.log(user['email']);   // "alice@example.com"

const { name, age, email } = user;
console.log(name); // "Alice"

// With renaming
const { name: userName } = user;

// With default values
const { role = 'viewer' } = user;

// Array destructuring
const [first, second] = ['a', 'b', 'c'];
// first = 'a', second = 'b'

const defaults = { theme: 'light', language: 'en', notifications: true };
const userPrefs = { theme: 'dark' };

const settings = { ...defaults, ...userPrefs };
// { theme: 'dark', language: 'en', notifications: true }

const scores = { math: 90, science: 85, english: 92 };

Object.keys(scores);    // ['math', 'science', 'english']
Object.values(scores);  // [90, 85, 92]
Object.entries(scores); // [['math', 90], ['science', 85], ['english', 92]]

for (const [subject, score] of Object.entries(scores)) {
  console.log(`${subject}: ${score}`);
}

const user = { address: { city: 'London' } };

console.log(user.address.city);        // "London"
console.log(user.address?.zip);        // undefined (no crash)
console.log(user.contact?.phone);      // undefined (no crash)

const value = null;
const result = value ?? 'default';  // "default"

const zero = 0;
const check = zero ?? 'default';    // 0 (not "default" — ?? only triggers on null/undefined)