JavaScript
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What is the output?
Anonymous Quiz
23%
10 30
40%
20 30
16%
20 20
21%
30 30
CHALLENGE

let order = [];
function a() {
try {
return 'try';
} finally {
order.push('a-finally');
return 'a-final-return';
}
}
function b() {
try {
throw new Error('x');
} catch (e) {
order.push('b-catch');
return 'b-catch-return';
} finally {
order.push('b-finally');
}
}
console.log(a(), b(), order.join(','));
❤1🔥1
CHALLENGE

const order = [];
order.push('start');
setTimeout(() => { order.push('timeout'); console.log(order.join(',')); }, 0);
Promise.resolve().then(() => order.push('promise1'));
async function foo() {
order.push('foo start');
await null;
order.push('foo end');
}
foo();
Promise.resolve().then(() => order.push('promise2'));
order.push('end');
❤2🔥1
CHALLENGE

const message = 'a😀bc';
const codePoints = [...message];
const combined = {
raw: message.length,
points: codePoints.length,
second: codePoints[1]
};
console.log(combined.raw, combined.points, combined.second);
❤1
❤2
CHALLENGE

class Counter {
#count = 0;
static #instances = 0;
constructor() { Counter.#instances++; }
#increment() { this.#count++; }
incrementAndGet() {
this.#increment();
return this.#count;
}
static get total() { return Counter.#instances; }
}

class SpecialCounter extends Counter {
incrementAndGet() {
return super.incrementAndGet() * 2;
}
}

const c1 = new Counter();
const c2 = new SpecialCounter();
console.log(`${c1.incrementAndGet()} ${c2.incrementAndGet()} ${Counter.total}`);
🤣2
What is the output?
Anonymous Quiz
18%
1 2 1
42%
1 4 2
23%
2 2 2
17%
1 2 2
❤2
CHALLENGE

const arr = [1, 2, 3];
const log = [];
const result = arr.map((x, i) => {
if (i === 0) arr.push(4);
log.push(x);
return x * 2;
});
console.log(result.join(','), log.join(','), arr.join(','));
❤3👍1
😮 How Anthropic Made Claude's Apps 3x Faster in Two Weeks

A grab bag of performance lessons from a sprint that cut p75 'time-to-typeable' from 3.1s to 0.55s. Em dashes (the irony!) pushed V8 onto a slower regex path, a stray location.reload() caused half a million hidden reloads a day, and more.

Wang, Attard, and G (Anthropic)
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❤1👍1