Prototype pollution 🥃
Exposing the default prototype by calling unsafe recursive functions with untrusted data as input
Read ~20mins estimated
learn.snyk.io
Exposing the default prototype by calling unsafe recursive functions with untrusted data as input
Read ~20mins estimated
learn.snyk.io
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❤9👍4🔥2
CHALLENGE
console.log('1');
setTimeout(() => console.log('2'), 0);
Promise.resolve().then(() => console.log('3'));
setTimeout(() => console.log('4'), 0);
Promise.resolve().then(() => {
console.log('5');
return Promise.resolve();
}).then(() => console.log('6'));
console.log('7');What is the output?
Anonymous Quiz
37%
1 7 3 5 6 2 4
25%
1 7 3 5 2 4 6
22%
1 7 2 4 3 5 6
15%
1 3 5 6 7 2 4
❤6👍3🤔1
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❤3👍3🔥2
CHALLENGE
const nums = [1, 2, 3];
const obj = { a: 1, b: 2, c: 3 };
function process(...args) {
const [first, ...rest] = args;
const { a, ...others } = obj;
return { first, rest, a, others };
}
const result = process(...nums);
console.log(result.first);
console.log(result.rest.length);
console.log(result.others.b);
console.log(Object.keys(result.others).join(''));
console.log(result.a === nums[0]);
❤4👍1
What is the output?
Anonymous Quiz
24%
1 3 2 bc true
29%
3 2 2 bc true
17%
1 2 2 bc false
30%
1 2 2 bc true
❤6👍3🤔3
CHALLENGE
let obj = { name: 'Sarah', age: 25 };
let weakMap = new WeakMap();
let map = new Map();
weakMap.set(obj, 'weak reference');
map.set(obj, 'strong reference');
console.log(weakMap.has(obj));
console.log(map.has(obj));
obj = null;
console.log(weakMap.has(null));
console.log(map.has(null));
console.log(map.size);❤1
What is the output?
Anonymous Quiz
30%
true true true true 1
39%
true true false false 1
22%
true true false false 0
9%
false false false false 0
2❤3👍2🔥1
CHALLENGE
function* fibonacci() {
let [a, b] = [0, 1];
while (true) {
yield a;
[a, b] = [b, a + b];
}
}
function* takeWhile(generator, predicate) {
for (const value of generator) {
if (!predicate(value)) break;
yield value;
}
}
const fib = fibonacci();
const smallFibs = takeWhile(fib, x => x < 20);
console.log([...smallFibs].join(','));👍3❤1
What is the output?
Anonymous Quiz
28%
1,1,2,3,5,8,13,21
36%
0,1,1,2,3,5,8,13,21
32%
0,1,1,2,3,5,8,13
4%
0,1,2,3,5,8,13
❤3🔥3👍1🤔1
Porffor is a rapidly developing ahead-of-time JavaScript compiler with a major benefit being extremely quick process launch times (think sub-millisecond). This is certainly more a taste of the future, and something to experiment with, rather than something you want to imminently deploy into production.
Oliver Medhurst
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👍7❤4🔥1
CHALLENGE
const user = {
name: 'Sarah',
age: 25,
getName() { return this.name; },
getAge: () => this.age
};
const methods = {
regular: user.getName,
arrow: user.getAge
};
console.log(methods.regular());
console.log(methods.arrow());
console.log(user.getName());
console.log(user.getAge());❤1
What is the output?
Anonymous Quiz
22%
Sarah undefined Sarah 25
32%
undefined undefined Sarah undefined
35%
Sarah 25 Sarah 25
11%
undefined 25 Sarah undefined
❤7🔥5🤔1
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❤11🤩6🤔5
CHALLENGE
let obj1 = { name: 'Sarah' };
let obj2 = { name: 'Mike' };
let obj3 = { ref: obj1 };
obj1.circular = obj1;
obj2.partner = obj3;
obj3.partner = obj2;
let weakMap = new WeakMap();
weakMap.set(obj1, 'data1');
weakMap.set(obj2, 'data2');
obj1 = null;
obj2 = null;
console.log(weakMap.has(obj3.ref));
console.log(obj3.partner.name);❤5
What is the output?
Anonymous Quiz
24%
false Mike
35%
true undefined
26%
true Mike
15%
false undefined
❤2👍2🔥2
If Linus Torvalds applied for a junior coding job today…
He’d get rejected.
He doesn’t have “5 years React experience.”
That’s how broken hiring has become.😨
He’d get rejected.
He doesn’t have “5 years React experience.”
That’s how broken hiring has become.
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🤣17🔥14❤3🤩1
CHALLENGE
function createCounter() {
let count = 0;
return {
increment: () => ++count,
decrement: () => --count,
get: () => count
};
}
const counter1 = createCounter();
const counter2 = createCounter();
counter1.increment();
counter1.increment();
counter2.increment();
console.log(counter1.get(), counter2.get());
const { increment, get } = counter1;
increment();
console.log(get());👍5❤3🔥1
CHALLENGE
const promise1 = Promise.resolve('first');
const promise2 = new Promise(resolve => {
resolve('second');
});
const promise3 = Promise.resolve().then(() => 'third');
async function test() {
console.log('start');
const result1 = await promise1;
console.log(result1);
const result2 = await promise2;
console.log(result2);
const result3 = await promise3;
console.log(result3);
console.log('end');
}
test();❤3