JavaScript

07 October 2025 15:04

💻 How Deno Protects Against npm Exploits

The maintainers of the Deno runtime reflect on the recent npm ecosystem security issues and show off how Deno’s non-permissive explicit ‘secure by default’ model can help.

Andy Jiang

JavaScript

06 October 2025 08:31

CHALLENGE

function createCounter() {
  let count = 0;
  return function(increment = 1) {
    count += increment;
    return count;
  };
}

const counter1 = createCounter();
const counter2 = createCounter();

console.log(counter1());
console.log(counter1(5));
console.log(counter2(3));
console.log(counter1());
console.log(counter2());

JavaScript

04 October 2025 08:32

CHALLENGE

class DataProcessor {
  constructor(value) {
    this.value = value;
  }
  
  transform(fn) {
    return new DataProcessor(fn(this.value));
  }
  
  getValue() {
    return this.value;
  }
}

const multiply = x => x * 2;
const add = x => x + 10;
const square = x => x * x;

const result = new DataProcessor(5)
  .transform(multiply)
  .transform(add)
  .transform(square)
  .getValue();

console.log(result);

JavaScript

03 October 2025 08:33

CHALLENGE

class Animal {
  constructor(name) {
    this.name = name;
  }
  speak() {
    return `${this.name} makes a sound`;
  }
}

class Dog extends Animal {
  speak() {
    return super.speak() + ' and barks';
  }
}

const pet = new Dog('Rex');
console.log(pet.speak());
console.log(pet instanceof Animal);
console.log(pet.constructor.name);

JavaScript

01 October 2025 16:16

🔥 n8n will change your life as a developer...

JavaScript

01 October 2025 00:07

🤟 A Year of Improving Node.js Compatibility in Cloudflare Workers

“We’ve been busy,” says Cloudflare which recently announced it’s bringing Node.js HTTP server support to its Workers function platform. This post goes deep into the technicalities, covering what areas of the standard library is supported, how the file system works (Workers doesn’t have a typical file system), how input/output streams work, and more. And you can use all of this now.

James M Snell (Cloudflare)

JavaScript

29 September 2025 15:01

👀 Give Your AI Eyes: Introducing Chrome DevTools MCP

The Chrome team has released an MCP server for Chrome DevTools, enabling agents like Claude Code or OpenAI Codex to use the DevTools to debug and analyze the performance and behavior of your webapps (or even just to automate the use of Chrome generally). Addy does a great job of explaining the potential here.

Addy Osmani

JavaScript

28 September 2025 08:31

CHALLENGE

const target = { name: 'Sarah', age: 25 };
const handler = {
  get(obj, prop) {
    if (prop === 'toString') {
      return () => `Person: ${obj.name}`;
    }
    return Reflect.get(obj, prop);
  },
  has(obj, prop) {
    return prop !== 'age' && Reflect.has(obj, prop);
  }
};
const proxy = new Proxy(target, handler);
console.log(proxy.name);
console.log('age' in proxy);
console.log(proxy.toString());

JavaScript

26 September 2025 15:05

😆

JavaScript

25 September 2025 08:30

CHALLENGE

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

try {
  throw new CustomError('Something went wrong', 500);
} catch (error) {
  console.log(error instanceof Error);
  console.log(error instanceof CustomError);
  console.log(error.name);
  console.log(typeof error.code);
}

JavaScript

23 September 2025 15:04

⛽️ npm-check-updates 18.2: Update package.json Dependencies to Latest Versions

That is, as opposed to the specified versions. Includes a handy -i interactive mode so you can look at potential upgrades and then opt in to them one by one. v18.2 adds a ‘cooldown’ feature to help protect against supply chain attacks by requiring package versions to be published at least the given number of days before considering them for upgrade.

Raine Revere

JavaScript

22 September 2025 15:01

🥳 IINA is a popular, open-source media player for macOS and it has just added a JavaScript-based plugin system to let users extend its functionality.

JavaScript

21 September 2025 15:04

⛽️ Massive Supply Chain Attack Hijacks ctrl/tinycolor With 2 Million Downloads and Other 40 NPM Packages

A sophisticated and widespread supply chain attack has struck the NPM ecosystem, compromising the popular @ctrl/tinycolor package, which is downloaded over 2 million times per week.

Guru Baran

JavaScript

20 September 2025 15:04

🤩 Fetch Streams are Great, But Not for Measuring Upload/Download Progress

Fetch upload streams seem well-suited for tracking the progress of uploads, but as Jake notes “just because stuff is taken from the stream doesn’t mean it’s yet been sent over the network”. He also touches on an issue relating to measuring download progress using response streams.

Jake Archibald

JavaScript

19 September 2025 19:46

👀 The 'Shai-Hulud' npm Supply Chain Attack Rumbles On

Now named after a term for the sandworms of the Dune universe, the ongoing malicious supply chain attack affecting the npm ecosystem has grown in scale with hundreds of packages affected in an attempt to exfiltrate tokens and secrets from developers’ machines.

Pandya, van der Zee, and Brown (Socket)

JavaScript

07 October 2025 08:32

CHALLENGE

const arr = [1, 2, 3, 4, 5];
const obj = { a: 1, b: 2, c: 3 };

const result1 = Object.keys(obj).length;
const result2 = arr.length;

delete obj.b;
obj.d = 4;

const result3 = Object.keys(obj).length;
const result4 = arr.push(6);

arr.length = 3;

const result5 = arr.length;
const result6 = Object.keys(obj).join('');

console.log(result1, result2, result3, result4, result5, result6);

JavaScript

05 October 2025 08:31

CHALLENGE

const Flyable = {
  fly() { return 'flying'; }
};

const Swimmable = {
  swim() { return 'swimming'; }
};

function mixin(Base, ...mixins) {
  mixins.forEach(mixin => Object.assign(Base.prototype, mixin));
  return Base;
}

class Bird {}
class Fish {}

const FlyingFish = mixin(class extends Fish {}, Flyable, Swimmable);
const instance = new FlyingFish();
console.log(instance.swim());
console.log(instance.fly());
console.log(instance instanceof Fish);

JavaScript

03 October 2025 21:04

✌️ The State of JavaScript 2025 Survey

Each year, Devographics runs an epic survey of as many JavaScript community members as it can and turns the results into an interesting report on the state of the ecosystem – here’s the results from 2024. If you have the time, fill it in, especially as they format it in a way where you can actually learn about stuff as you go.

Devographics

JavaScript

02 October 2025 08:31

CHALLENGE

class EventEmitter {
  constructor() { this.events = {}; }
  on(event, fn) { (this.events[event] ||= []).push(fn); }
  emit(event, data) { this.events[event]?.forEach(fn => fn(data)); }
}

class Logger {
  log(msg) { console.log(`LOG: ${msg}`); }
}

class Counter {
  constructor() { this.count = 0; }
  increment() { this.count++; console.log(this.count); }
}

function withLogging(target) {
  const logger = new Logger();
  return new Proxy(target, {
    get(obj, prop) {
      if (typeof obj[prop] === 'function') {
        return function(...args) {
          logger.log(`calling ${prop}`);
          return obj[prop].apply(obj, args);
        };
      }
      return obj[prop];
    }
  });
}

const emitter = withLogging(new EventEmitter());
const counter = new Counter();
emitter.on('tick', () => counter.increment());
emitter.emit('tick');
emitter.emit('tick');

JavaScript

01 October 2025 10:33

CHALLENGE

function processData() {
  try {
    console.log('processing');
    return 'success';
  } catch (error) {
    console.log('error caught');
    return 'failed';
  } finally {
    console.log('cleanup');
  }
}

const result = processData();
console.log('result:', result);

JavaScript

30 September 2025 08:32

CHALLENGE

console.log('1');

Promise.resolve().then(() => {
  console.log('2');
  Promise.resolve().then(() => console.log('3'));
});

Promise.resolve().then(() => {
  console.log('4');
});

setTimeout(() => console.log('5'), 0);

console.log('6');

JavaScript

29 September 2025 08:33

CHALLENGE

async function processData() {
  console.log('Start');
  
  const promise1 = new Promise(resolve => {
    console.log('Promise 1 executor');
    resolve('Result 1');
  });
  
  const promise2 = Promise.resolve('Result 2');
  console.log('After promises created');
  
  const result1 = await promise1;
  console.log(result1);
  
  const result2 = await promise2;
  console.log(result2);
  
  return 'Done';
}

processData().then(result => console.log(result));

JavaScript

27 September 2025 08:33

CHALLENGE

class StateMachine {
  constructor() {
    this.state = 'idle';
    this.transitions = {
      idle: { start: 'running', reset: 'idle' },
      running: { pause: 'paused', stop: 'stopped' },
      paused: { resume: 'running', stop: 'stopped' },
      stopped: { reset: 'idle' }
    };
  }
  
  transition(action) {
    const nextState = this.transitions[this.state]?.[action];
    if (nextState) {
      this.state = nextState;
      return true;
    }
    return false;
  }
}

const sm = new StateMachine();
console.log(sm.transition('start'));
console.log(sm.state);
console.log(sm.transition('reset'));
console.log(sm.state);

JavaScript

26 September 2025 08:31

CHALLENGE

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

function processData(data) {
  try {
    if (!data) throw new ValidationError('Data required', 'MISSING_DATA');
    return data.toUpperCase();
  } catch (error) {
    if (error instanceof ValidationError) {
      console.log(`${error.name}: ${error.message} (${error.code})`);
    } else {
      console.log(`Unexpected error: ${error.message}`);
    }
  }
}

processData(null);
processData(42);

JavaScript

24 September 2025 08:33

CHALLENGE

let cache = new Map();
let obj = { name: 'Emma', age: 28 };

function memoize(fn) {
  return function(...args) {
    const key = JSON.stringify(args);
    if (cache.has(key)) {
      console.log('Cache hit');
      return cache.get(key);
    }
    const result = fn.apply(this, args);
    cache.set(key, result);
    return result;
  };
}

const process = memoize((data) => {
  console.log('Processing:', data.name);
  return data.age * 2;
});

process(obj);
process(obj);
obj.age = 30;
process(obj);
console.log('Cache size:', cache.size);

JavaScript

23 September 2025 08:31

CHALLENGE

const pattern = /(?<=\d)(?=(?:\d{3})+(?!\d))/g;
const str = '1234567890';
const result = str.replace(pattern, ',');
console.log(result);

const regex = /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[a-zA-Z\d]{8,}$/;
const tests = ['Password1', 'password', 'PASSWORD1', 'Pass1'];
tests.forEach(test => {
  console.log(`${test}: ${regex.test(test)}`);
});

const capture = /([a-z]+)(\d+)/g;
const text = 'item123 product456';
const matches = [...text.matchAll(capture)];
console.log(matches[1][1]);

JavaScript

22 September 2025 08:32

CHALLENGE

const sym1 = Symbol('test');
const sym2 = Symbol('test');
const obj = {
  [sym1]: 'value1',
  [sym2]: 'value2',
  regular: 'value3'
};

const sym3 = Symbol.for('global');
const sym4 = Symbol.for('global');

console.log(sym1 === sym2);
console.log(sym3 === sym4);
console.log(Object.keys(obj).length);
console.log(Object.getOwnPropertySymbols(obj).length);

JavaScript

21 September 2025 08:33

CHALLENGE

const cache = new Map();

function createHandler(id) {
  const data = { id, value: new Array(1000).fill(id) };
  cache.set(id, data);
  
  return function(action) {
    if (action === 'get') return data;
    if (action === 'clear') cache.delete(id);
  };
}

const handler1 = createHandler('user-1');
const handler2 = createHandler('user-2');

handler1('clear');
console.log(cache.size);
console.log(handler1('get').id);

JavaScript

20 September 2025 08:30

CHALLENGE

const nums = [1, 2, 3, 4, 5];
const result = nums
  .filter(n => n > 2)
  .map(n => n * 2)
  .reduce((acc, n) => {
    acc.push(n + 1);
    return acc;
  }, [])
  .slice(1);

console.log(result);
console.log(nums);

JavaScript

19 September 2025 08:35

CHALLENGE

const moduleCache = new Map();

async function loadModule(name) {
  if (moduleCache.has(name)) {
    return moduleCache.get(name);
  }
  
  const module = await Promise.resolve({
    default: () => `Module ${name} loaded`,
    version: '1.0.0'
  });
  
  moduleCache.set(name, module);
  return module;
}

const results = [];
loadModule('auth').then(m => results.push(m.default()));
loadModule('auth').then(m => results.push(m.version));
loadModule('utils').then(m => results.push(m.default()));

setTimeout(() => console.log(results.join(', ')), 0);