class Session {
  #id;
  constructor(id) {
    this.#id = id;
  }
  getId() { return this.#id; }
}

const activeSessions = new WeakSet();

const s1 = new Session("user_42");
const s2 = new Session("user_99");
let s3 = new Session("user_07");

activeSessions.add(s1);
activeSessions.add(s2);
activeSessions.add(s3);

console.log(activeSessions.has(s1));         // line A
console.log(activeSessions.has(s3));         // line B

s3 = null;

console.log(activeSessions.has(s3));         // line C

activeSessions.delete(s2);
console.log(activeSessions.has(s2));         // line D
console.log(activeSessions.size);            // line E

const inventory = {
  apples: 5,
  bananas: 0,
  cherries: 12,
  dates: undefined,
  elderberries: null,
};

const summary = Object.entries(inventory)
  .filter(([_, value]) => value)
  .reduce((acc, [key, value]) => {
    acc[key] = value * 2;
    return acc;
  }, {});

console.log(Object.keys(summary).length);
console.log(Object.values(summary).every(v => v > 10));
console.log(Object.keys(inventory).length === Object.keys(summary).length);

const user = {
  profile: {
    getName: () => "Marcus",
    getAge: () => 30,
  },
  settings: null,
};

const name = user.profile?.getName?.();
const age = user.profile?.getAge?.();
const theme = user.settings?.getTheme?.() ?? "dark";
const lang = user.address?.getLocale?.() ?? "en-US";

console.log(`${name} | ${age} | ${theme} | ${lang}`);

let x = 'global';

function testScope() {
  console.log(x);
  
  if (true) {
    let x = 'block';
    var y = 'function';
    console.log(x);
  }
  
  console.log(x);
  console.log(y);
}

testScope();

const name = "Zara";
const age = 28;
const role = "engineer";

const user = { name, age, role };

const { name: fullName, age: years, role: position = "developer" } = user;

const greet = ({ name, age }) => `${name} is ${age}`;

const team = [
  { name: "Zara", age: 28 },
  { name: "Leo",  age: 34 },
];

const [{ name: first }, { age: secondAge }] = team;

console.log(`${fullName}, ${years}, ${position} | ${first}, ${secondAge}`);

const a = 10n ** 3n;
const b = BigInt(Number.MAX_SAFE_INTEGER) + 1n;
const c = b - BigInt(Number.MAX_SAFE_INTEGER);

const results = {
  power: a,
  safe: c,
  type: typeof a,
  equal: 10n == 10,
  strict: 10n === 10,
};

console.log(
  results.power,
  results.safe,
  results.type,
  results.equal,
  results.strict
);

class Registry {
  static #cache = new Map();
  static #instanceCount = 0;
  static defaultTTL;

  static {
    Registry.#cache.set("base", { value: 42, active: true });
    Registry.#instanceCount = 1;
    Registry.defaultTTL = 3600;
    console.log("Static block 1:", Registry.#instanceCount, Registry.defaultTTL);
  }

  static {
    const base = Registry.#cache.get("base");
    Registry.#cache.set("derived", { value: base.value * 2, active: false });
    Registry.#instanceCount++;
    console.log("Static block 2:", Registry.#instanceCount, Registry.#cache.size);
  }

  static getSnapshot() {
    return [...Registry.#cache.entries()]
      .map(([k, v]) => `${k}:${v.value}`)
      .join(", ");
  }
}

console.log("Snapshot:", Registry.getSnapshot());
console.log("TTL:", Registry.defaultTTL);