What is the output?
Anonymous Quiz
30%
Hello, Sarah Hi, undefined
32%
Hello, undefined Hi, Sarah
11%
Hello, undefined Hi, undefined
27%
Hello, Sarah Hi, Sarah
❤7🤣4🤔2🔥1
CHALLENGE
class Observable {
constructor(subscribe) {
this.subscribe = subscribe;
}
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')
});❤3🤔2
What is the output?
Anonymous Quiz
32%
2 4 done
34%
2 4 complete
22%
undefined undefined done
12%
1 2 done
❤2👍2🔥2🤔2
From the same creators of the fantastic
CultRepo
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👍4🔥3❤1
CHALLENGE
const obj = {
name: 'Sarah',
greet() {
return `Hello, ${this.name}`;
},
delayedGreet() {
const fn = function() {
return this.greet();
};
return fn.call(this);
}
};
const result = obj.delayedGreet();
console.log(result);❤2
What is the output?
Anonymous Quiz
18%
Hello, undefined
26%
TypeError: this.greet is not a function
50%
Hello, Sarah
6%
undefined
❤4👍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));❤3
❤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')
});What is the output?
Anonymous Quiz
17%
1 2 done
56%
2 4 done
18%
undefined undefined done
9%
[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
44%
true false true true bigint true
28%
false true true false number true
5%
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
31%
third second third true undefined
29%
third second first true 2
33%
first second third true 3
7%
first second first false undefined
🔥3❤1👍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');
}❤1👍1🔥1