What is the output?
Anonymous Quiz
32%
[1, 5, 4, true]
28%
[1, 4, 4, false]
27%
[1, 5, 4, false]
13%
[1, 5, 5, true]
❤2👍2🔥2🤔1
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);
});
What is the output?
Anonymous Quiz
39%
20 20 [25, 60]
24%
10 10 [15, 30]
19%
10 20 [25, 60]
17%
20 25 [25, 60]
❤3👍3🤔2🤩2
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);
❤3
❤10
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);👍3❤1
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);❤3
What is the output?
Anonymous Quiz
17%
2 2 1 false false
46%
3 3 1 true false
25%
1 2 1 true false
12%
3 3 3 true true
❤5👍4
⚠️ 🔵 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
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
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👍3🤔2
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);❤1
👍3❤1🤩1
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
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❤3🤔2
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);