JavaScript

const handler = {
  get(target, prop, receiver) {
    if (prop === 'fullName') {
      return `${Reflect.get(target, 'firstName', receiver)} ${Reflect.get(target, 'lastName', receiver)}`;
    }
    return Reflect.get(target, prop, receiver);
  },
  set(target, prop, value, receiver) {
    if (typeof value !== 'string') {
      return false;
    }
    return Reflect.set(target, prop, value.trim(), receiver);
  },
  has(target, prop) {
    return prop.startsWith('_') ? false : Reflect.has(target, prop);
  }
};

const person = new Proxy({ firstName: '  Clara', lastName: 'Oswald  ', _secret: 'hidden' }, handler);
person.firstName = '  Clara';
person.lastName = '  Oswald';

console.log(person.fullName);
console.log('_secret' in person);
console.log(Reflect.ownKeys(person).length);

const inventory = {
  apples: 5,
  bananas: 12,
  cherries: 0,
  dates: 8,
};

const result = Object.entries(inventory)
  .filter(([_, qty]) => qty > 0)
  .reduce((acc, [fruit, qty]) => {
    acc[fruit] = qty * 2;
    return acc;
  }, {});

const keys = Object.keys(result);
const values = Object.values(result);

console.log(keys.length, values.reduce((sum, v) => sum + v, 0));

class AppError extends Error {
  constructor(message, code) {
    super(message);
    this.name = "AppError";
    this.code = code;
  }
}

function riskyOperation(value) {
  if (value === null) throw new AppError("Null value", 404);
  if (typeof value !== "number") throw new TypeError("Not a number");
  if (value < 0) throw new RangeError("Negative value");
  return value * 2;
}

const inputs = [42, null, "hello", -5];
const results = inputs.map((input) => {
  try {
    return riskyOperation(input);
  } catch (err) {
    if (err instanceof AppError) return `AppError:${err.code}`;
    if (err instanceof TypeError) return `TypeError`;
    if (err instanceof RangeError) return `RangeError`;
    return `UnknownError`;
  }
});

console.log(results);

const transactions = [
  { id: 1, type: "credit", amount: 200 },
  { id: 2, type: "debit",  amount: 50  },
  { id: 3, type: "credit", amount: 150 },
  { id: 4, type: "debit",  amount: 30  },
  { id: 5, type: "credit", amount: 100 },
];

const result = transactions
  .filter(tx => tx.type === "credit")
  .map(tx => ({ ...tx, amount: tx.amount * 1.1 }))
  .reduce((acc, tx) => acc + tx.amount, 0);

console.log(result.toFixed(2));

const product = {
  name: "Laptop",
  price: 1299,
  stock: 42,
  discount: 0,
  category: "Electronics",
};

const filtered = Object.entries(product)
  .filter(([key, value]) => Boolean(value))
  .reduce((acc, [key, value]) => {
    acc[key] = value;
    return acc;
  }, {});

console.log(Object.keys(filtered).length);
console.log(Object.values(filtered).includes(0));
console.log(Object.keys(filtered).join(", "));

const engine = {
  type: "V8",
  displacement: 4.0,
  getInfo() {
    return `${this.type} - ${this.displacement}L`;
  },
  turbo: {
    boost: 12,
    getBoost() {
      return `${this.type ?? "Unknown"} boosted at ${this.boost} psi`;
    },
  },
};

const detached = engine.getInfo;
const turboInfo = engine.turbo.getBoost;

console.log(engine.getInfo());
console.log(engine.turbo.getBoost());
console.log(turboInfo());

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);

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
);