function Dashboard(){
  const [data,setData]=useState(null);
  useEffect(()=>{fetch('/api/items').then(r=>r.json()).then(setData)},[]);
  function save(item){fetch('/api/items', {method:'POST', body:JSON.stringify(item)})}
  return <div>{data?.map(i=><div key={i.id}>{i.name}</div>)}</div>
}

function useFetch(url){
  const [data,setData]=useState(null);
  useEffect(()=>{fetch(url).then(r=>r.json()).then(setData)},[url]);
  return data;
}
function DashboardView({data}){ return <div>{data?.map(i=><div key={i.id}>{i.name}</div>)}</div> }
function Dashboard(){ const data=useFetch('/api/items'); return <DashboardView data={data}/> }

// controller
async function createItem(req,res){ const item=await itemService.create(req.body); res.json(item) }
// service
async function create(data){ validate(data); return repository.insert(data) }

npm install fastify

const fastify = require('fastify')({ logger: true })

fastify.get('/', async (request, reply) => {
  return { hello: 'world' }
})

fastify.listen({ port: 3000 })
  .then(() => console.log('listening on 3000'))
  .catch(err => fastify.log.error(err))

npx create-next-app@latest my-app
cd my-app
npm run dev

export default function Home() {
  return <h1>سلام Next.js 👋</h1>
}

const nums = [3, 12, 2, 21, 5];

function multiply(arr, factor = 2) {
  arr.sort();
  factor = 10;
  return arr
    .map((n, i) => n * (factor - i))
    .join("-");
}

console.log(multiply(nums));
console.log(nums.join(","));

/* حالت پیش‌فرض (Light) */
:root {
  --bg: #ffffff;
  --fg: #111827;
}

/* وقتی Dark Mode فعاله */
html.dark {
  --bg: #0f172a;
  --fg: #e5e7eb;
}

body {
  background-color: var(--bg);
  color: var(--fg);
  transition: background-color 150ms ease, color 150ms ease;
}

const root = document.documentElement;

function toggleTheme() {
  root.classList.toggle('dark');
}

function outer() {
  const result = [];

  const obj = {
    value: 10,
    normal: function (x) {
      result.push("normal:" + this.value + "," + arguments.length);
      (function () {
        result.push("iife:" + (this.value ?? "undefined"));
      })();
    },
    arrow: (y) => {
      result.push("arrow:" + (this.value ?? "undefined") + "," + (typeof arguments));
    }
  };

  obj.normal(1, 2);
  obj.arrow(3);

  return result.join(" | ");
}

console.log(outer());

// userService.js (لایه Domain / Use Case)
class UserService {
  constructor(userRepo) {
    this.userRepo = userRepo; // وابستگی به interface، نه به Express
  }

  async registerUser(data) {
    const { email, password } = data;

    if (!email || !password) {
      throw new Error("Invalid data");
    }

    const exists = await this.userRepo.findByEmail(email);
    if (exists) {
      throw new Error("Email already used");
    }

    // اینجا می‌توانید hashing، ruleها و ... را قرار دهید
    return this.userRepo.create({ email, password });
  }
}

module.exports = UserService;

// userRepo.js (لایه Infrastructure)
const users = [];

module.exports = {
  async findByEmail(email) {
    return users.find(u => u.email === email) || null;
  },
  async create(user) {
    users.push(user);
    return user;
  }
};

// routes.js
const express = require("express");
const UserService = require("./userService");
const userRepo = require("./userRepo");

const router = express.Router();
const userService = new UserService(userRepo);

router.post("/register", async (req, res) => {
  try {
    const user = await userService.registerUser(req.body);
    res.status(201).json(user);
  } catch (err) {
    res.status(400).json({ error: err.message });
  }
});

module.exports = router;