What is the output?
Anonymous Quiz
19%
Hello, undefined
24%
TypeError: this.greet is not a function
52%
Hello, Sarah
5%
undefined
❤5👍1🔥1🤔1🤩1
The author takes us back ten years to the genesis of Prettier, the popular opinionated, deterministic code formatter he co-created with James Long. Prettier effectively introduced and popularized the practice of fully-automated AST-based code formatting in the JavaScript ecosystem.
Christopher Chedeau (Vjeux)
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❤11👍2🔥1
CHALLENGE
class Calculator {
static multiply(a, b) {
return a * b;
}
static add = (a, b) => {
return a + b;
}
}
class ScientificCalculator extends Calculator {
static multiply(a, b) {
return super.multiply(a, b) * 2;
}
}
console.log(Calculator.multiply(3, 4));
console.log(ScientificCalculator.add(5, 6));
console.log(ScientificCalculator.multiply(2, 3));❤4
❤4🤔3👍2🔥2
Graphviz is a suite of open source graph drawing tools of over 30 years’ vintage. Viz.js is a WebAssembly Graphviz build that brings its functionality into the browser. GitHub repo.
Michael Daines
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❤6👍2🔥1
CHALLENGE
class Observable {
constructor(subscriber) {
this.subscriber = subscriber;
}
subscribe(observer) {
return this.subscriber(observer);
}
map(fn) {
return new Observable(observer => {
return this.subscribe({
next: value => observer.next(fn(value)),
error: err => observer.error(err),
complete: () => observer.complete()
});
});
}
}
const source = new Observable(observer => {
observer.next(1);
observer.next(2);
observer.complete();
});
const doubled = source.map(x => x * 2);
doubled.subscribe({
next: value => console.log(value),
complete: () => console.log('done')
});❤2
What is the output?
Anonymous Quiz
16%
1 2 done
53%
2 4 done
20%
undefined undefined done
11%
[object Object] [object Object] done
❤4👍1🔥1
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❤2👍1🔥1
CHALLENGE
const a = 9007199254740991n;
const b = BigInt(9007199254740991);
const c = 9007199254740992;
const d = BigInt(9007199254740992);
console.log(a === b);
console.log(Number(a) === c);
console.log(c === Number.MAX_SAFE_INTEGER + 1);
console.log(d > a);
console.log(typeof (a + 1n));
console.log(Number(d) === c);
What is the output?
Anonymous Quiz
22%
true true true true bigint true
41%
true false true true bigint true
29%
false true true false number true
9%
true true false true bigint false
❤3
CHALLENGE
const userInput = "<script>alert('xss')</script>";
const sanitized = userInput
.replace(/</g, '<')
.replace(/>/g, '>')
.replace(/"/g, '"')
.replace(/'/g, ''');
const credentials = {
username: 'admin',
password: 'secret123'
};
const safeLog = (obj) => {
const { password, ...safe } = obj;
return JSON.stringify(safe);
};
console.log(sanitized);
console.log(safeLog(credentials));CHALLENGE
const wm = new WeakMap();
const obj1 = {};
const obj2 = {};
const obj3 = obj1;
wm.set(obj1, 'first');
wm.set(obj2, 'second');
wm.set(obj3, 'third');
console.log(wm.get(obj1));
console.log(wm.get(obj2));
console.log(wm.get(obj3));
console.log(wm.has(obj1));
console.log(wm.size);
What is the output?
Anonymous Quiz
29%
third second third true undefined
25%
third second first true 2
36%
first second third true 3
11%
first second first false undefined
🔥3❤2👍1
CHALLENGE
const data = '{"name": "Maria", "age": 25, "skills": ["JavaScript", "Python"]}';
try {
const parsed = JSON.parse(data);
const modified = {
...parsed,
age: parsed.age + 5,
skills: [...parsed.skills, "TypeScript"]
};
const serialized = JSON.stringify(modified, null, 0);
const reparsed = JSON.parse(serialized);
console.log(reparsed.skills.length);
console.log(typeof reparsed.age);
} catch (error) {
console.log('Parse error');
}❤7
👍4🔥2🤔2❤1
CHALLENGE
const numbers = [1, 2, 3, 4, 5];
const pipeline = (...fns) => (value) => fns.reduce((acc, fn) => fn(acc), value);
const multiply = (x) => (y) => x * y;
const add = (x) => (y) => x + y;
const square = (x) => x * x;
const transform = pipeline(
multiply(2),
add(3),
square
);
const result = numbers.map(transform);
console.log(result);
👍6❤3
What is the output?
Anonymous Quiz
22%
[4, 16, 36, 64, 100]
54%
[25, 49, 81, 121, 169]
17%
[16, 36, 64, 100, 144]
6%
[9, 25, 49, 81, 121]
👍3❤2
The latest cutting edge version of Node has arrived with Web Storage enabled by default, JSON.stringify perf improvements, a new --allow-net option in the permission model, built-in Uint8Array base64/hex conversion, and WebAssembly and JIT optimizations. As shown in the diagram above, this means Node 24 will soon be promoted to being the 'active' LTS release and Node 22 will enter its 'maintenance' LTS phase.
Rafael Gonzaga
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CHALLENGE
function Vehicle(type) {
this.type = type;
}
Vehicle.prototype.describe = function() {
return `This is a ${this.type}`;
};
function Car(brand) {
Vehicle.call(this, 'car');
this.brand = brand;
}
Car.prototype = Object.create(Vehicle.prototype);
Car.prototype.constructor = Car;
Car.prototype.describe = function() {
return Vehicle.prototype.describe.call(this) + ` made by ${this.brand}`;
};
const tesla = new Car('Tesla');
console.log(tesla.describe());
console.log(tesla.constructor.name);❤2