JavaScript
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(' | '));
812 · 📊 Quiz
What is the output?
- undefined | Cannot access 'bar' before initialization
- undefined | undefined
- function | Cannot access 'bar' before initialization
- undefined | ReferenceError: Cannot access 'bar' before initialization
votes: 113 · results after voting — in Telegram ↗
JavaScript
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);
533 · 📊 Quiz
What is the output?
- [ 1, 2, 3, 4, [ 5, 6 ] ] [ 1, 2, 3, 4, 5, 6 ] [ [1,1], [2,3], [4,[5,6]] ]
- [ 1, 2, 3, 4, [ 5, 6 ] ] [ 1, 2, 3, 4, 5, 6 ] [ 1, 1, 2, 3, 4, [ 5, 6 ] ]
- [ 1, 2, 3, 4, [ 5, 6 ] ] [ 1, 2, 3, 4, 5, 6 ] [ 1, 2, 3, 4, [ 5, 6 ] ]
- [ 1, 2, 3, 4, 5, 6 ] [ 1, 2, 3, 4, 5, 6 ] [ 1, 1, 2, 3, 4, [ 5, 6 ] ]
votes: 114 · results after voting — in Telegram ↗
JavaScript
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);
❤1
1.3K · 📊 Quiz
What is the output?
- 1 11 undefined 100
- 1 11 100 undefined
- 1 11 100 100
- 1 10 100 undefined
votes: 93 · results after voting — in Telegram ↗
❤2🔥2🤔1
1.7K · JavaScript
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 })
);
1.2K · 📊 Quiz
What is the output?
- 42 42 7 99
- 42 100 7 99
- 42 42 42 42
- undefined 42 7 99
votes: 90 · results after voting — in Telegram ↗
❤4
1.7K · Photo
💻 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
❤2👍1🤔1
1 · 1.1K · JavaScript
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));
❤3
1 · 1.1K · 📊 Quiz
What is the output?
- [ 10, 11 ] []
- [ 10, 6 ] undefined
- [ 10, 6 ] []
- [ 5, 6 ] []
votes: 89 · results after voting — in Telegram ↗
🤩1
1.8K · Photo
🤟 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
❤6👍1
5 · 1.1K · JavaScript
CHALLENGE
const x = 0;
const y = '';
const z = null;
const r1 = x ?? y ? 'A' : 'B';
const r2 = z ?? y ? 'C' : 'D';
console.log(r1, r2);
903 · JavaScript
CHALLENGE
async function run() {
const results = await Promise.allSettled([
Promise.resolve(1),
Promise.reject('error'),
new Promise(resolve => setTimeout(() => resolve(3), 0)),
]);
console.log(results.map(r => r.value ?? r.reason).join(','));
}
run();
1 · 741 · 📊 Quiz
What is the output?
- 3,error,1
- 1,error,3
- error,1,3
- 1,undefined,3
votes: 113 · results after voting — in Telegram ↗
JavaScript
CHALLENGE
class Counter {
#count = 0;
get value() {
return this.#count;
}
set value(v) {
if (v < this.#count) throw new RangeError('Cannot decrease');
this.#count = v;
}
}
const c = new Counter();
c.value = 5;
let msg;
try {
c.value = 3;
} catch (e) {
msg = e.message;
}
c.value = 10;
console.log(msg, c.value);
413 · 📊 Quiz
What is the output?
- RangeError 10
- Cannot decrease 10
- undefined 10
- Cannot decrease 3
votes: 106 · results after voting — in Telegram ↗
JavaScript
CHALLENGE
const obj = { b: 1, 2: 'two', a: 3, 1: 'one' };
console.log(Object.keys(obj).join(','), Object.values(obj).join(','));
1 · 859 · 📊 Quiz
What is the output?
- 1,2,a,b one,two,3,1
- b,2,a,1 1,two,3,one
- 1,2,b,a one,two,1,3
- a,b,1,2 3,1,one,two
votes: 121 · results after voting — in Telegram ↗
❤6👍1
1.6K · JavaScript
CHALLENGE
class Counter {
static #total = 0;
#id;
constructor() {
Counter.#total++;
this.#id = Counter.#total;
}
get id() { return this.#id; }
static get total() { return Counter.#total; }
}
class Special extends Counter {
#label;
constructor(label) {
super();
this.#label = label;
}
get label() { return `${this.#label}-${this.id}`; }
}
const c1 = new Counter();
const c2 = new Special('x');
const c3 = new Special('y');
console.log(c1.id, c2.id, c3.label, Counter.total);
660 · 📊 Quiz
What is the output?
- 1 2 x-3 3
- 1 1 y-3 3
- 1 2 y-3 2
- 1 2 y-3 3
votes: 108 · results after voting — in Telegram ↗
JavaScript
CHALLENGE
const source = {
count: 0,
get value() {
this.count++;
return this.count;
}
};
const { value, ...rest } = source;
const spread = { ...source };
console.log(value, spread.value, source.count, JSON.stringify(rest));
200 · 📊 Quiz
What is the output?
- 1 2 2 {"count":1}
- 1 2 1 {"count":0}
- 2 2 2 {"count":2}
- 1 1 1 {"count":1}
votes: 113 · results after voting — in Telegram ↗
JavaScript
📊 Quiz
What is the output?
- 1 2 2 1 2
- 1 2 1 2 2
- 1 2 1 1 2
- 1 1 1 1 2
votes: 62 · results after voting — in Telegram ↗
❤1
554 ·