JavaScript

CHALLENGE

const compose = (...fns) => (x) => fns.reduceRight((acc, fn) => fn(acc), x);
const pipe = (...fns) => (x) => fns.reduce((acc, fn) => fn(acc), x);

const double = (x) => x * 2;
const addTen = (x) => x + 10;
const square = (x) => x ** 2;
const negate = (x) => -x;

const transform1 = compose(negate, square, addTen, double);
const transform2 = pipe(double, addTen, square, negate);

const memoize = (fn) => {
  const cache = new Map();
  return (x) => {
    if (!cache.has(x)) cache.set(x, fn(x));
    return cache.get(x);
  };
};

const memoTransform1 = memoize(transform1);

console.log(transform1(3));
console.log(transform2(3));
console.log(memoTransform1(3) === transform1(3));

👀 Remix 3 Enters Beta — It's No Longer a React Framework Remix has quite the back story. Created by the duo behind React Router in 2020 and seen as an alternative to Next.js, Remix was acquired by Shopify in 2022 and its core ideas folded into React Router v7 in 2024. Now, a new direction: a full-stack, web standards-first framework with its own UI component model and… no React. Michael Jackson (Remix)

CHALLENGE

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

class ConnectionError extends DatabaseError {
  constructor(host) {
    super(`Failed to connect to ${host}`, 503);
    this.name = "ConnectionError";
    this.host = host;
  }
}

const err = new ConnectionError("db.server.io");

console.log([
  err instanceof ConnectionError,
  err instanceof DatabaseError,
  err instanceof Error,
  err.name,
  err.code,
  err.message,
].join(" | "));

😮 html-to-text 10.0: Advanced HTML to Text Converter Uses a variety of techniques to convert even complex HTML into plain text (but with some formatting, such as for tables). v10 brings the project up to modern standards. KillyMXI

CHALLENGE

const items = [
  { name: "banana", price: 1.5, qty: 10 },
  { name: "apple",  price: 1.5, qty: 5  },
  { name: "cherry", price: 3.0, qty: 8  },
  { name: "date",   price: 2.0, qty: 8  },
];

const sorted = [...items].sort((a, b) => {
  if (a.price !== b.price) return a.price - b.price;
  if (a.qty   !== b.qty)   return b.qty   - a.qty;
  return a.name.localeCompare(b.name);
});

console.log(sorted.map(i => `${i.name}:${i.qty}`).join(", "));

🤟 Node.js 26.0 (Current) Released It's here! Complete with the Temporal API enabled by default, V8 14.6 (say hello to map ‘upsert’ methods like Map.prototype.getOrInsert() and iterator sequencing with Iterator.concat()), plus Undici 8. v26 is the ‘Current’ cutting-edge release until October when it gets promoted to LTS. Rafael Gonzaga

CHALLENGE

const values = [0.1 + 0.2, NaN, Infinity, -0, 42.6789];

const results = values.map((v, i) => {
  if (i === 0) return Number.isInteger(v) + " | " + v.toFixed(2);
  if (i === 1) return Number.isFinite(v) + " | " + Number.isNaN(v);
  if (i === 2) return Number.isFinite(v) + " | " + Number.MAX_SAFE_INTEGER;
  if (i === 3) return Object.is(v, -0) + " | " + (v === 0);
  if (i === 4) return v.toFixed(2) + " | " + v.toPrecision(4);
});

results.forEach(r => console.log(r));

CHALLENGE

const ops = {
  add: (a, b) => a + b,
  subtract: (a, b) => a - b,
  multiply: (a, b) => a * b,
  divide: (a, b) => b !== 0 ? a / b : NaN,
};

const pipeline = (...fns) => (value) => fns.reduce((acc, fn) => fn(acc), value);

const double  = (x) => ops.multiply(x, 2);
const addTen  = (x) => ops.add(x, 10);
const halve   = (x) => ops.divide(x, 2);
const subtractThree = (x) => ops.subtract(x, 3);

const transform = pipeline(double, addTen, halve, subtractThree);

const results = [5, 0, -4].map(transform);
console.log(results);

CHALLENGE

const inventory = new Map([
  ["sword", { quantity: 3, weight: 15 }],
  ["shield", { quantity: 1, weight: 25 }],
  ["potion", { quantity: 10, weight: 2 }],
]);

inventory.set("bow", { quantity: 2, weight: 8 });
inventory.delete("shield");

const totalWeight = [...inventory.entries()].reduce((acc, [item, { quantity, weight }]) => {
  return acc + quantity * weight;
}, 0);

const heaviestItem = [...inventory.entries()].reduce((max, [item, data]) =>
  data.weight > max.weight ? { name: item, ...data } : max,
  { name: "", weight: 0 }
);

console.log(inventory.size, totalWeight, heaviestItem.name);

CHALLENGE

const delay = (ms, val) => new Promise(res => setTimeout(res, ms, val));

async function pipeline(...fns) {
  return async (input) => {
    let result = input;
    for (const fn of fns) {
      result = await fn(result);
    }
    return result;
  };
}

const double  = async (x) => delay(10, x * 2);
const addTen  = async (x) => delay(10, x + 10);
const square  = async (x) => delay(10, x ** 2);

(async () => {
  const process = await pipeline(double, addTen, square);
  const output  = await process(3);
  console.log(output);
})();

CHALLENGE

class Vehicle {
  #speed = 0;

  constructor(brand) {
    this.brand = brand;
  }

  accelerate(amount) {
    this.#speed += amount;
    return this;
  }

  getSpeed() {
    return this.#speed;
  }

  toString() {
    return `${this.brand} @ ${this.#speed}km/h`;
  }
}

class Car extends Vehicle {
  #gear = 1;

  constructor(brand, model) {
    super(brand);
    this.model = model;
  }

  shiftUp() {
    this.#gear++;
    return this;
  }

  toString() {
    return `${super.toString()} [Gear ${this.#gear}]`;
  }
}

const car = new Car("Toyota", "Supra");
car.accelerate(60).accelerate(40).shiftUp().shiftUp();

console.log(car.toString());
console.log(car instanceof Car);
console.log(car instanceof Vehicle);
console.log(Object.getPrototypeOf(Car) === Vehicle);