CHALLENGE
class EventManager {
constructor() {
this.listeners = new Map();
}
addListener(event, callback) {
if (!this.listeners.has(event)) {
this.listeners.set(event, new Set());
}
this.listeners.get(event).add(callback);
}
removeAllListeners() {
this.listeners.clear();
}
}
const manager = new EventManager();
const obj = { data: new Array(1000).fill('memory') };
manager.addListener('test', () => obj.data.length);
manager.removeAllListeners();
console.log(manager.listeners.size);🔥2❤1👍1
The Vite-powered, Jest-compatible testing framework introduces visual regression testing, makes its ‘Browser Mode’ stable (for running tests in a browser directly), adds Playwright Traces support, and more. Still unsure? You can compare it with other test runners here.
VoidZero and Contributors
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❤4👍2🔥1
CHALLENGE
async function fetchData() {
return Promise.resolve('data');
}
async function processData() {
const result = await fetchData();
console.log('Processing:', result);
return result.toUpperCase();
}
const promise = processData();
console.log('Promise:', promise);
promise.then(value => {
console.log('Final:', value);
});CHALLENGE
class DataProcessor {
constructor(transform) {
this.transform = transform;
}
process(data) {
return this.transform(data);
}
}
const multiply = x => x * 2;
const addTen = x => x + 10;
const toString = x => `Result: ${x}`;
const compose = (...fns) => x => fns.reduceRight((acc, fn) => fn(acc), x);
const processor = new DataProcessor(compose(toString, addTen, multiply));
console.log(processor.process(5));❤2🔥2
❤4👍2🔥1
It’s been more than four years since we linked to Sindre's handy resource, but it continues to get updates and tweaks (and, if you want, you can contribute a submission too – though the bar is quite high).
Sindre Sorhus
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CHALLENGE
const target = { name: 'Sarah', age: 25 };
const handler = {
get(obj, prop) {
if (prop in obj) {
return obj[prop].toString().toUpperCase();
}
return `Property ${prop} not found`;
},
set(obj, prop, value) {
obj[prop] = value * 2;
return true;
}
};
const proxy = new Proxy(target, handler);
proxy.salary = 50000;
console.log(proxy.name);
console.log(proxy.age);
console.log(proxy.salary);
console.log(proxy.city);What is the output?
Anonymous Quiz
46%
SARAH 25 100000 Property city not found
40%
SARAH 25 50000 Property city not found
11%
Sarah 25 50000 undefined
2%
Sarah age salary city
🔥3❤1👍1
CHALLENGE
function highlight(strings, ...values) {
return strings.reduce((result, string, i) => {
const value = values[i] ? `<mark>${values[i]}</mark>` : '';
return result + string + value;
}, '');
}
const name = 'Sarah';
const skill = 'React';
const template = highlight`Hello ${name}, you're great at ${skill}!`;
console.log(template);CHALLENGE
const str = 'JavaScript';
const result1 = str.slice(-6, -2);
const result2 = str.substring(-6, -2);
const result3 = str.substr(-6, 4);
const combined = [result1, result2, result3];
const final = combined.map(s => s || 'empty').join(' | ');
console.log(final);
What is the output?
Anonymous Quiz
25%
Scri | JavaScript | Scri
37%
Script | empty | Script
31%
Scri | empty | Scri
7%
Scri | | Scri
🤔7❤3👍1🔥1
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First there was the "use strict" directive to opt in to strict mode in JavaScript, but now you’ll encounter use client, use server, React's new use no memo, and more, and they're not standard JS features at all. Tanner thinks this proliferation of directives comes at a cost, with an increased risk of framework and tooling lock-in.
Tanner Linsley (TanStack)
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CHALLENGE
const user = {
name: 'Sarah',
age: 28,
city: 'Boston'
};
const keys = Object.keys(user);
const values = Object.values(user);
const entries = Object.entries(user);
const result = entries.map(([key, value]) => {
return typeof value === 'string' ? key.toUpperCase() : value * 2;
});
console.log(result);❤7🔥2👍1
What is the output?
Anonymous Quiz
31%
['SARAH', 28, 'BOSTON']
43%
['NAME', 56, 'CITY']
18%
[undefined, 56, undefined]
7%
['NAME', 'CITY', 56]
❤4
It’s not often we see a library with such a funny demo on the homepage (it involves cats and laser pointers!) Navcat is a pathfinding library, aimed at games and simulations, for enabling objects to route through 3D space. There are numerous other interesting demos too. GitHub repo.
Isaac Mason
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CHALLENGE
const numbers = [1, 2, 3, 4, 5];
const result = numbers
.filter(n => n % 2 === 0)
.map(n => n * 2)
.reduce((acc, n) => acc + n, 0);
const original = numbers.slice();
original.reverse();
const flattened = [[1, 2], [3], [4, 5]].flat();
const found = flattened.find(n => n > 3);
console.log(result);
console.log(original.length);
console.log(found);
❤2
👍8❤2🔥1