JavaScript

27 December 2025 14:03

✌️ The JavaScript Bundler Grand Prix

Bundlers now sit at the heart of many JavaScript workflows and are sometimes even integrated into runtimes (e.g. Bun’s). This piece surveys the landscape and argues the speed wars are mostly over, with the real battle shifting to artifact size and the code that actually ships to users.

Kate Holterhoff

JavaScript

26 December 2025 14:05

🌟 Anthropic just bought your favorite JS runtime...

🔥 Fireship

JavaScript

24 December 2025 00:02

Merry Christmas 🎄

JavaScript

22 December 2025 07:30

CHALLENGE

const x = 5;
const y = 10;

const result = `${x + y}`;
const nested = `Value: ${`${x}` + `${y}`}`;
const expr = `${x}${y}`;

console.log(result);
console.log(nested);
console.log(expr);
console.log(typeof result);

JavaScript

20 December 2025 09:19

💎 Sponsored

Gold quietly hit a new record in 2025 🚀

Some assets move fast, others move steadily, but both say something about how we react to risk.

How well do you read these shifts?

Check yourself by taking a short quiz.

JavaScript

19 December 2025 07:32

CHALLENGE

const json = '{"name":"Sarah","age":25,"active":true}';
const obj = JSON.parse(json);

obj.name = "Emma";
obj.age++;

const json2 = JSON.stringify(obj);
const obj2 = JSON.parse(json2);

obj.age = 100;

console.log(obj2.age);

JavaScript

17 December 2025 07:31

CHALLENGE

const x = null;
const y = undefined;
const z = 0;

const result1 = x ?? 'default';
const result2 = y ?? 'default';
const result3 = z ?? 'default';

const combined = result1 ? result2 ? result3 : 'B' : 'C';

console.log(combined);

JavaScript

16 December 2025 07:33

CHALLENGE

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

Vehicle.prototype.wheels = 4;
Vehicle.prototype.getInfo = function() {
  return `${this.type}: ${this.wheels}`;
};

const car = new Vehicle('Car');
const bike = Object.create(car);
bike.type = 'Bike';
bike.wheels = 2;

console.log(car.getInfo() + ' | ' + bike.getInfo());

JavaScript

14 December 2025 07:31

CHALLENGE

const obj = { a: 1, b: 2, c: 3 };
Object.defineProperty(obj, 'd', { 
  value: 4, 
  enumerable: false 
});

const entries = Object.entries(obj);
const keys = Object.keys(obj);
const values = Object.values(obj);

console.log(entries.length + keys.length + values.length);

JavaScript

13 December 2025 07:33

CHALLENGE

class Subject {
  constructor() {
    this.observers = [];
  }
  attach(observer) {
    this.observers.push(observer);
  }
  notify(data) {
    this.observers.forEach(obs => obs.update(data));
  }
}

const subject = new Subject();
subject.attach({ update: (d) => console.log(d * 2) });
subject.attach({ update: (d) => console.log(d + 5) });
subject.notify(10);

JavaScript

12 December 2025 07:32

CHALLENGE

const a = { x: 1 };
const b = a;
const c = { x: 1 };

b.x = 2;
const d = b;
d.x = 3;

console.log(a.x);
console.log(b.x);
console.log(c.x);
console.log(a === b);
console.log(a === c);

JavaScript

10 December 2025 07:33

CHALLENGE

const x = 5;
const y = 10;

const obj = {
  x,
  y,
  z: x + y,
  calculate() {
    return this.x * this.y;
  },
  [x + y]: 'computed'
};

console.log(obj.calculate() + obj[15] + obj.z);

JavaScript

08 December 2025 07:31

CHALLENGE

const map = new Map([
  ['a', 1],
  ['b', 2],
  ['c', 3]
]);

const key = { id: 'key' };
map.set(key, 4);
map.set(key, 5);

const result = [];
result.push(map.get('a'));
result.push(map.get(key));
result.push(map.size);
result.push(map.has({ id: 'key' }));

console.log(result);

JavaScript

06 December 2025 07:31

CHALLENGE

class EventEmitter {
  constructor() {
    this.events = {};
  }
  
  on(event, callback) {
    this.events[event] = this.events[event] || [];
    this.events[event].push(callback);
    return this;
  }
  
  emit(event, data) {
    if (this.events[event]) {
      this.events[event].forEach(cb => cb(data));
    }
    return this;
  }
}

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

JavaScript

04 December 2025 07:33

CHALLENGE

class Logger {
  log(msg) {
    return `[LOG]: ${msg}`;
  }
}

class Formatter {
  format(text) {
    return text.toUpperCase();
  }
}

class Service {
  constructor(logger, formatter) {
    this.logger = logger;
    this.formatter = formatter;
  }
  
  process(data) {
    const formatted = this.formatter.format(data);
    return this.logger.log(formatted);
  }
}

const service = new Service(new Logger(), new Formatter());
console.log(service.process('hello world'));

JavaScript

27 December 2025 07:31

CHALLENGE

const getValue = (x) => {
  console.log(`Getting: ${x}`);
  return x;
};

const obj = { name: null };

const result = obj.name || getValue('default') && getValue('final');
console.log(`Result: ${result}`);

JavaScript

26 December 2025 07:32

CHALLENGE

const numbers = [1, 2, 3, 4, 5];
const result = numbers
  .filter(n => n % 2 === 0)
  .map(n => n * 2)
  .reduce((acc, curr) => acc + curr, 0);

const original = numbers.slice();
numbers.splice(2, 1, 99);

console.log(result);
console.log(numbers);
console.log(original);

JavaScript

23 December 2025 07:30

CHALLENGE

const obj = Object.seal({ a: 1, b: { c: 2 } });
obj.a = 10;
obj.b.c = 20;
obj.d = 30;
delete obj.a;

const frozen = Object.freeze({ x: 5, y: { z: 10 } });
frozen.x = 50;
frozen.y.z = 100;
delete frozen.y;

console.log(obj.a, obj.b.c, obj.d, frozen.x, frozen.y.z);

JavaScript

21 December 2025 07:33

CHALLENGE

const x = 0.1 + 0.2;
const y = 0.3;

console.log(x === y);
console.log(x.toFixed(1) === y.toFixed(1));
console.log(+x.toFixed(1) === +y.toFixed(1));

const num = 42;
console.log(num.toString(2));
console.log(parseInt('101010', 2));

JavaScript

20 December 2025 07:30

CHALLENGE

const multiplier = 3;

function createCounter() {
  let count = 0;
  const multiplier = 5;
  
  return function() {
    count++;
    return count * multiplier;
  };
}

const counter = createCounter();
console.log(counter());
console.log(counter());
console.log(multiplier);

JavaScript

18 December 2025 07:32

CHALLENGE

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

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

const car = new Vehicle('Car');
const bike = Vehicle('Bike');

console.log(car.describe());
console.log(typeof bike);
console.log(globalThis.type);

JavaScript

16 December 2025 14:05

🤔 Open Sourcing the Remix Store

The Remix Store is a swag store for the Remix project and its codebase provides a powerful example of how Remix’s own core team builds apps with Remix and Hydrogen.

Brooks Lybrand and the Remix Team

JavaScript

14 December 2025 19:00

👀 Useful Patterns for Building HTML Tools

In many situations, you don’t need a full-on framework to build useful tools; just HTML, JavaScript and CSS in a single file will do the job fine. Simon’s become a bit of an expert by rolling out many such tools using LLMs, and shares his process and practices here. More please!

Simon Willison

JavaScript

13 December 2025 13:10

👀 Many Devs blame Vercel for Next.js-related React security vulnerabilities.

Because making new frameworks like Next.js is relatively easy nowadays, someone with enough social influence can literally destroy Vercel's business by popularising some other framework, which, by the way, would have nearly identical problems anyway, because this was mostly the React problem itself.

Tigran Bayburtsyan

JavaScript

12 December 2025 07:57

⚠️ 🔵 Denial of Service and Source Code Exposure in React Server Components

Security researchers have found and disclosed two additional vulnerabilities in React Server Components while attempting to exploit the patches in last week’s critical vulnerability.

If you already updated for the Critical Security Vulnerability last week, you will need to update again.

If you updated to 19.0.2, 19.1.3, and 19.2.2, these are incomplete and you will need to update again.

December 11, 2025 by The React Team

JavaScript

11 December 2025 07:30

CHALLENGE

const curry = (fn) => {
  return function curried(...args) {
    if (args.length >= fn.length) {
      return fn.apply(this, args);
    }
    return (...nextArgs) => curried(...args, ...nextArgs);
  };
};

const multiply = (a, b, c) => a * b * c;
const curriedMultiply = curry(multiply);

const step1 = curriedMultiply(2);
const step2 = step1(3);
const result = step2(4);

console.log(result);

JavaScript

09 December 2025 07:31

CHALLENGE

const promise1 = Promise.resolve(10);
const promise2 = promise1.then(x => x * 2);
const promise3 = promise2.then(x => {
  console.log(x);
  return x + 5;
});
const promise4 = promise2.then(x => {
  console.log(x);
  return x * 3;
});
Promise.all([promise3, promise4]).then(results => {
  console.log(results);
});

JavaScript

06 December 2025 22:48

🎉 JavaScript Turns 30 Years Old

Back in May 1995, a 33 year old Brendan Eich built the first prototype of JavaScript in just ten days, originally codenamed Mocha (and then LiveScript). On December 4, 1995, Netscape and Sun Microsystems officially announced 'JavaScript' in a press release as "an easy-to-use object scripting language designed for creating live online applications that link together objects and resources on both clients and servers."

Over thirty years, JavaScript has cemented its place at the heart of the Web platform, and more broadly in desktop apps, operating systems (e.g. Windows' use of React Native), mobile apps, and even on microcontrollers.

JavaScript

05 December 2025 07:31

CHALLENGE

let obj1 = { name: 'Sarah' };
let obj2 = { name: 'Mike' };

obj1.ref = obj2;
obj2.ref = obj1;

let weakRef = new WeakRef(obj1);
let registry = new FinalizationRegistry((value) => {
  console.log(`Cleanup: ${value}`);
});

registry.register(obj1, 'obj1-cleaned');
obj1 = null;
obj2 = null;

console.log(weakRef.deref()?.name || 'undefined');
console.log('Script completed');

JavaScript

03 December 2025 07:32

CHALLENGE

const data = '{"users": [{"name": "Sarah", "age": 25}, {"name": "Mike", "age": null}]}';

try {
  const parsed = JSON.parse(data);
  const result = parsed.users.map(user => {
    return user.age ?? 'unknown';
  });
  console.log(result.join(' - '));
} catch (error) {
  console.log('Parse error occurred');
}

const invalidJson = '{"name": "John", age: 30}';
try {
  JSON.parse(invalidJson);
  console.log('Success');
} catch {
  console.log('Invalid');
}