JavaScript

🤟 You Don’t Know Node.js EventLoop (30 min read) You might be wondering if the title of this article is a bit ambitious, but fear not! I’ve put in the time and effort to cover everything you need to know about the EventLoop in Node.js. And believe me, you’ll discover so many new things along the way! nairihar

CHALLENGE

class EventBus {
  #listeners = new Map();
  on(event, cb) {
    if (!this.#listeners.has(event)) this.#listeners.set(event, []);
    this.#listeners.get(event).push(cb);
    return this;
  }
  emit(event, ...args) {
    const cbs = this.#listeners.get(event) || [];
    return cbs.map(cb => cb(...args));
  }
}

const bus = new EventBus();
bus.on('data', x => x * 2).on('data', x => x + 1);
const results = bus.emit('data', 5);
console.log(results, bus.emit('missing', 1));

💻 Deno is Joining Cloudflare (But…) Maybe David Bushell saw the writing on the wall, as the Deno team isn't joining Cloudflare to keep working on Deno, but to fold celld into workerd so Durable Objects can be self-hosted (more on that here). The Deno runtime will get a final year of official fixes, Deno Deploy closes in six months, and JSR moves to Cloudflare's infrastructure. Ryan Dahl

CHALLENGE

const obj = {
  value: 42,
  getValue: function() {
    return this.value;
  }
};

const unboundGetValue = obj.getValue;
const boundGetValue = unboundGetValue.bind(obj);
const boundTwice = boundGetValue.bind({ value: 100 });

console.log(
  boundGetValue(),
  boundTwice(),
  unboundGetValue.call({ value: 7 }),
  obj.getValue.apply({ value: 99 })
);

CHALLENGE

function* inner() {
  const x = yield 1;
  yield x + 1;
  return 100;
}

function* outer() {
  const result = yield* inner();
  yield result;
}

const g = outer();
console.log(g.next().value, g.next(10).value, g.next().value, g.next().value);

CHALLENGE

const arr = [1, [2, 3], [4, [5, 6]]];
const a = arr.flat();
const b = arr.flat(Infinity);
const c = arr.flatMap(x => Array.isArray(x) ? x : [x, x]);
console.log(a, b, c);

CHALLENGE

const output = [];
output.push(typeof foo);
try {
  output.push(typeof bar);
} catch (e) {
  output.push(e.message);
}
var foo = () => 'foo';
let bar = () => 'bar';
console.log(output.join(' | '));

CHALLENGE

async function main() {
  const settled = await Promise.allSettled([
    Promise.resolve(1),
    Promise.reject('err'),
  ]);
  const statuses = settled.map(s => s.status).join(',');

  let anyResult;
  try {
    await Promise.any([Promise.reject('a'), Promise.reject('b')]);
  } catch (err) {
    anyResult = `${err.name}:${err.errors.join(',')}`;
  }

  console.log(statuses, anyResult);
}

main();

CHALLENGE

const a = -7 % 3;
const b = 7 % -3;
const c = 2 ** 3 ** 2;
const d = (2 ** 3) ** 2;
const e = 0.1 + 0.2;
console.log(a, b, c, d, e);

CHALLENGE

function tag(strings, ...values) {
  return strings.raw.join('|') + '::' + values.join(',');
}

const a = 5, b = 10;
console.log(tag`Sum:\n${a + b} End`);

CHALLENGE

const sym1 = Symbol('id');
const sym2 = Symbol('id');

const obj = {
  [sym1]: 'first',
  [sym2]: 'second',
  regular: 'value'
};

const s = Symbol.for('shared');
const s2 = Symbol.for('shared');

console.log(
  sym1 === sym2,
  Object.keys(obj).length,
  Reflect.ownKeys(obj).length,
  s === s2,
  sym1.toString()
);