Modern JavaScript (ES6+)

let age = 28;
age = 29;               // let বদলায়

const pi = 3.14;
// pi = 3;             // const বদলায় না

const user = { name: "রহিম" };
user.age = 30;          // object-এর property বদলায় — ঠিক আছে
// user = {};           // reference বদলায় না

const add = (a, b) => a + b;
const double = (x) => x * 2;

console.log(add(2, 3));  // 5
console.log(double(4));  // 8

const name = "রহিম";
const age = 28;

const sentence = `আমার নাম ${name}, বয়স ${age}।`;
console.log(sentence); // আমার নাম রহিম, বয়স 28।

// Array
const [first, second] = [10, 20, 30];
console.log(first, second); // 10 20

// Object
const user = { name: "রহিম", age: 28 };
const { name, age } = user;
console.log(name, age); // রহিম 28

// Default
const { city = "ঢাকা" } = user;
console.log(city); // ঢাকা

// Spread — ফেলা
const nums = [3, 4];
const combined = [1, 2, ...nums, 5];
console.log(combined); // [1, 2, 3, 4, 5]

const base = { a: 1, b: 2 };
const copy = { ...base, c: 3 };
console.log(copy); // { a: 1, b: 2, c: 3 }

// Rest — জমানো
function sum(...args) {
  return args.reduce((t, n) => t + n, 0);
}
console.log(sum(1, 2, 3, 4)); // 10

function greet(name = "অতিথি") {
  return `নমস্কার, ${name}!`;
}
console.log(greet());      // নমস্কার, অতিথি!
console.log(greet("রহিম")); // নমস্কার, রহিম!

const user = { address: { city: "ঢাকা" } };

console.log(user.address?.city); // ঢাকা
console.log(user.phone?.number); // undefined (crash নয়)

const count = null ?? 10;
const zero = 0 ?? 99;
console.log(count, zero); // 10 0

class Animal {
  constructor(name) {
    this.name = name;
  }
  speak() {
    return `${this.name} শব্দ করছে`;
  }
}

class Dog extends Animal {
  speak() {
    return super.speak() + " — ঘেউ";
  }
}

const dog = new Dog("টমি");
console.log(dog.speak()); // টমি শব্দ করছে — ঘেউ

// math.js
export function add(a, b) {
  return a + b;
}

export default function multiply(a, b) {
  return a * b;
}

// app.js
import multiply, { add } from "./math.js";

console.log(add(2, 3));       // 5
console.log(multiply(2, 3));   // 6

async function load() {
  const res = await fetch("/api/users");
  const data = await res.json();
  console.log(data);
}

// call
load().catch(console.error);