JavaScript

26 March 2026 07:31

CHALLENGE

const obj = {
  name: "Orion",
  greet() {
    const inner = () => {
      console.log(this.name);
    };
    inner();
  },
  greetRegular: function () {
    const inner = function () {
      console.log(this?.name ?? "undefined");
    };
    inner();
  },
};

obj.greet();
obj.greetRegular();

JavaScript

24 March 2026 07:33

CHALLENGE

const compose = (...fns) => fns.reduce((f, g) => (...args) => f(g(...args)));

const pipe = (...fns) => fns.reduce((f, g) => (...args) => g(f(...args)));

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

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

const val = 3;

console.log(transform1(val), transform2(val));

JavaScript

22 March 2026 07:31

CHALLENGE

const temperature = {
  celsius: 22,
  [Symbol.toPrimitive](hint) {
    if (hint === 'number') {
      return this.celsius;
    }
    if (hint === 'string') {
      return `${this.celsius}°C`;
    }
    return this.celsius + 273.15;
  }
};

console.log(`Temp: ${temperature}`);
console.log(temperature + 0);
console.log(temperature * 2);
console.log(+temperature);

JavaScript

21 March 2026 07:31

CHALLENGE

class EventEmitter {
  #listeners = new WeakMap();
  #registry = new FinalizationRegistry((label) => {
    console.log(`Cleaned up: ${label}`);
  });

  subscribe(target, callback) {
    if (!this.#listeners.has(target)) {
      this.#listeners.set(target, []);
    }
    this.#listeners.get(target).push(callback);
    this.#registry.register(target, target.name ?? "unknown");
  }

  emit(target) {
    const cbs = this.#listeners.get(target);
    if (cbs) cbs.forEach(cb => cb());
  }
}

const emitter = new EventEmitter();
let obj1 = { name: "sensor" };
let obj2 = { name: "timer" };

const ws = new WeakSet([obj1, obj2]);

emitter.subscribe(obj1, () => console.log("sensor fired"));
emitter.subscribe(obj2, () => console.log("timer fired"));
emitter.subscribe(obj1, () => console.log("sensor logged"));

emitter.emit(obj1);

console.log(ws.has(obj1));
obj1 = null;
console.log(ws.has({ name: "sensor" }));

JavaScript

20 March 2026 07:32

CHALLENGE

function Vehicle(make, model, year) {
  this.make = make;
  this.model = model;
  this.year = year;
  this.describe = function () {
    return `${this.year} ${this.make} ${this.model}`;
  };
}

Vehicle.prototype.age = function (currentYear) {
  return currentYear - this.year;
};

const car = new Vehicle("Toyota", "Supra", 1998);
const bike = new Vehicle("Harley", "Sportster", 2005);

console.log(car.describe());
console.log(bike.age(2025));
console.log(car.constructor === Vehicle);
console.log(Object.getPrototypeOf(car) === Vehicle.prototype);

JavaScript

19 March 2026 07:32

CHALLENGE

const p1 = new Promise((resolve) => {
  console.log("A");
  resolve("B");
});

const p2 = p1.then((val) => {
  console.log(val);
  return "C";
});

p2.then((val) => {
  console.log(val);
});

console.log("D");

JavaScript

18 March 2026 07:31

CHALLENGE

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

class ValidationError extends AppError {
  constructor(message) {
    super(message, 400);
    this.fields = [];
  }
}

function riskyOperation(value) {
  if (value === null) throw new ValidationError("Null value");
  if (value < 0) throw new AppError("Negative value", 422);
  return value * 2;
}

const results = [];

for (const val of [10, null, -5, 3]) {
  try {
    results.push(riskyOperation(val));
  } catch (e) {
    if (e instanceof ValidationError) {
      results.push(`Validation:${e.statusCode}`);
    } else if (e instanceof AppError) {
      results.push(`App:${e.statusCode}`);
    } else {
      results.push("Unknown");
    }
  }
}

console.log(results.join(" | "));

JavaScript

16 March 2026 07:30

CHALLENGE

"use strict";

function createCounter() {
  let count = 0;

  return {
    increment() { count++; },
    decrement() { count--; },
    getCount() { return count; },
    reset: () => { count = 0; }
  };
}

const counter = createCounter();
counter.increment();
counter.increment();
counter.increment();
counter.decrement();

const { getCount, reset } = counter;

console.log(getCount());
reset();
console.log(counter.getCount());

JavaScript

29 January 2026 13:12

🤔 Porting 100k Lines from TypeScript to Rust in a Month

A prolific JavaScript developer ported a Pokémon battle simulator to Rust and shares his experiences and techniques used to work around issues where Claude Code would get bogged down in such a large task. He notes “LLM-based coding agents are such a great new tool” but require “engineering expertise and constant babysitting”.

Christopher Chedeau

JavaScript

28 January 2026 13:12

👀 Introducing LibPDF: PDF Parsing and Generation from TypeScript

LibPDF bills itself as ‘the PDF library TypeScript deserves’ and supports parsing, modifying, signing and generating PDFs with a modern API in Node, Bun, and the browser. GitHub repo.

Documenso

JavaScript

27 January 2026 07:35

CHALLENGE

const obj = {
  data: ['x', 'y', 'z'],
  *[Symbol.iterator]() {
    for (let i = this.data.length - 1; i >= 0; i--) {
      yield this.data[i].toUpperCase();
    }
  }
};

const result = [];
for (const item of obj) {
  result.push(item);
  if (result.length === 2) break;
}

console.log(result.join('-'));

JavaScript

25 January 2026 07:31

CHALLENGE

class Calculator {
  constructor(value) {
    this.value = value;
  }
  
  add(num) {
    this.value += num;
    return this;
  }
  
  multiply(num) {
    this.value *= num;
    return this;
  }
}

const calc = new Calculator(5);
const addMethod = calc.add;
const result = addMethod.call(calc, 3).multiply(2);
console.log(result.value);

JavaScript

24 January 2026 07:30

CHALLENGE

function processData() {
  const results = [];
  
  for (let i = 0; i < 3; i++) {
    const multiplier = i + 1;
    
    setTimeout(() => {
      results.push(i * multiplier);
    }, 0);
  }
  
  setTimeout(() => {
    console.log(results.join(','));
  }, 10);
}

processData();

JavaScript

23 January 2026 07:31

CHALLENGE

function* innerGenerator() {
  yield 1;
  yield 2;
  return 'inner-done';
}

function* outerGenerator() {
  yield 'start';
  const result = yield* innerGenerator();
  yield result;
  yield 'end';
}

const gen = outerGenerator();
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next().value);

JavaScript

22 January 2026 07:33

CHALLENGE

function Vehicle(type) {
  this.type = type;
  this.wheels = 4;
}

Vehicle.prototype.getInfo = function() {
  return `${this.type} with ${this.wheels} wheels`;
};

const car = new Vehicle('sedan');
const bike = Vehicle('motorcycle');

console.log(car.getInfo());
console.log(typeof bike);
console.log(bike?.type || 'undefined');

JavaScript

25 March 2026 05:49

🥶 Announcing TypeScript 6.0

Over six months in the making, TypeScript 6.0 is designed to bridge the gap between its self-hosted compiler and the (almost ready) Go-powered native compiler of TypeScript 7.0 .

There are new features (Temporal improvements, RegExp.escape, and more), but most important are the changes to help you prepare for 7.0:

• Numerous default changes: strict is now true, module is esnext, rootDir defaults to ., and more.
• A change that will affect many apps is types defaulting to [] rather than pulling in everything from node_modules/@types.
• Numerous deprecations: the es5 target, emitting AMD, UMD, and SystemJS modules, --baseUrl, and others.
• --stableTypeOrdering makes 6.0's type ordering behavior match 7.0's to help diagnose inference differences as you update.

Daniel Rosenwasser (Microsoft)

JavaScript

23 March 2026 07:32

CHALLENGE

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

console.log(typeof a);
console.log(a === 1000n);
console.log(b === c);
console.log(5n / 2n);

JavaScript

21 March 2026 14:01

🤟 Evolving the Node.js Release Schedule: A Work in Progress

The Node.js team has long been discussing shifting Node to a new schedule of one major release per year (instead of two), removing the odd/even distinction, and making every release LTS (with a prior 11 months of alpha/current status). This is a preview post not intended for final publication till April, so things are subject to change (backup version).

The Node.js Team

JavaScript

20 March 2026 14:33

🥶 Patreon has shared the tale of its seven year migration from JavaScript to TypeScript. There's a focus on tooling choices that might be useful if you're making a similar shift.

JavaScript

19 March 2026 14:32

📈 In The 49MB Web Page, Shubham Bose expresses surprise at finding that loading a single NY Times page results in 422 network requests and 49 megabytes of data transferred. He reflects on the problems that have led to this being a common experience on news sites.

JavaScript

18 March 2026 14:02

✌️ Temporal: The 9-Year Journey to Fix Time in JavaScript

JavaScript’s date/time handling is notoriously messy and libraries like Moment.js became popular as a way to work around it. In 2017, Maggie Johnson-Pint, a maintainer of Moment.js, proposed the Temporal API to fix date/time handling for good, and we’re mostly there (support is growing, with Safari and Node to catch up).

Jason Williams (Bloomberg)

JavaScript

17 March 2026 07:33

CHALLENGE

const p1 = new Promise((resolve) => {
  console.log("A");
  resolve("X");
});

const p2 = p1.then((val) => {
  console.log("B");
  return val + "Y";
});

const p3 = p2.then((val) => {
  console.log("C:", val);
});

console.log("D");

JavaScript

15 March 2026 13:04

🚨 𝟭𝟱𝟬+ 𝗚𝗶𝘁𝗛𝘂𝗯 𝗿𝗲𝗽𝗼𝘀𝗶𝘁𝗼𝗿𝗶𝗲𝘀 𝗰𝗼𝗺𝗽𝗿𝗼𝗺𝗶𝘀𝗲𝗱 𝗯𝘆 𝗚𝗹𝗮𝘀𝘀𝗪𝗼𝗿𝗺 𝗠𝗮𝗹𝘄𝗮𝗿𝗲

JavaScript

29 January 2026 07:31

CHALLENGE

const wm = new WeakMap();
let obj1 = { name: 'John' };
let obj2 = { name: 'Jane' };

wm.set(obj1, 'developer');
wm.set(obj2, 'designer');

console.log(wm.get(obj1));
console.log(wm.has(obj2));

obj1 = null;
console.log(wm.get(obj1));

const normalObj = {};
try {
  wm.set('string', 'value');
} catch (e) {
  console.log('error');
}

JavaScript

28 January 2026 07:31

CHALLENGE

const x = 15;
const y = 10;
const z = 3;

const result1 = x & y;
const result2 = x | y;
const result3 = x ^ y;
const result4 = ~x;
const result5 = y << z;
const result6 = y >> 1;

console.log(`${result1},${result2},${result3},${result4},${result5},${result6}`);

JavaScript

26 January 2026 07:32

CHALLENGE

class EventEmitter {
  constructor() {
    this.events = new Map();
  }
  
  on(event, callback) {
    if (!this.events.has(event)) {
      this.events.set(event, []);
    }
    this.events.get(event).push(callback);
    return this;
  }
  
  emit(event, ...args) {
    const callbacks = this.events.get(event);
    if (callbacks) {
      callbacks.forEach(cb => cb(...args));
    }
    return this;
  }
}

const emitter = new EventEmitter();
emitter.on('test', x => console.log(x * 2))
       .on('test', x => console.log(x + 10))
       .emit('test', 5);

JavaScript

24 January 2026 14:02

👀 Superdiff 4.0: Compares Arrays or Objects and Returns a Diff

Got two similar objects or arrays and want to see the underlying differences? Superdiff has been around a while, but recent updates boost performance, add support for streamed input and using a worker for more efficient diffing in a background thread. The project now has a handy documentation site too.

antoine

JavaScript

23 January 2026 14:04

Whether you agree or not, Ryan Dahl, the original creator of both Node.js and Deno, drew a lot of attention for a post on X (above) where he shared a thought on the shifting roles of modern software engineers in an agentic world.

JavaScript

22 January 2026 14:54

💎 Happy 20th Birthday jQuery!

On January 14, 2006, John Resig introduced a JavaScript library called jQuery at BarCamp in New York City....

Timmy Willison

JavaScript

21 January 2026 14:56

🤟 Node.js Becomes a First-Class Citizen in Microsoft Aspire

Aspire is a Microsoft framework for orchestrating the development and deployment of distributed applications. Originally just targeting .NET, the new Aspire 13 makes JavaScript a first-class citizen, so you can now run Vite, Node.js, and full-stack JS apps with service discovery, built-in telemetry, and production-ready containers.

Microsoft