Channel: JavaScript
A custom element that uses the CSS Custom Highlight API (supported by most modern browsers) for syntax highlighting so you don’t need to retreat to the age-old method of wrapping every token in spans.
André Ruffert
Please open Telegram to view this post
VIEW IN TELEGRAM
CHALLENGE
function processConfig(config) {
const settings = {
timeout: config.timeout ?? 1000,
retries: config.retries ?? 3,
logging: config.logging ?? false,
debug: config.debug || true
};
return settings;
}
const userConfig = {
timeout: 0,
retries: null,
logging: false,
debug: false
};
console.log(processConfig(userConfig));CHALLENGE
const createMathOps = (base) => {
return {
add: (x) => base + x,
multiply: (x) => base * x
};
};
const createAdvancedMathOps = (base) => {
const basicOps = createMathOps(base);
return {
...basicOps,
square: () => basicOps.multiply(base),
addThenSquare: (x) => {
const added = basicOps.add(x);
return added * added;
}
};
};
const calculator = createAdvancedMathOps(5);
console.log(calculator.addThenSquare(3));CHALLENGE
const obj = { name: 'Alice', age: 30 };
const handler = {
get(target, prop) {
return prop in target ? target[prop] : `Property '${prop}' doesn't exist`;
}
};
const proxy = new Proxy(obj, handler);
const descriptors = Object.getOwnPropertyDescriptors(obj);
Reflect.defineProperty(obj, 'city', {
value: 'New York',
enumerable: false
});
console.log(proxy.city, proxy.country);Adonis is a popular TypeScript-first 'batteries included' web framework with a rich set of features, and its developers say they’re “shifting gears” and stepping up with more frequent major releases. v7 promises a lot, including Node.js diagnostic channel support, a type-safe URL builder, a new encryption layer, first-class support for notifications and TanStack Query, plus more. You’re encouraged to give your feedback here.
Romain Lanz
Please open Telegram to view this post
VIEW IN TELEGRAM
CHALLENGE
const text = 'Today is 2023-12-31 and tomorrow is 2024-01-01';
const dateRegex = /(\d{4})-(\d{2})-(\d{2})/g;
let result = '';
let match;
while ((match = dateRegex.exec(text)) !== null) {
const [fullMatch, year, month, day] = match;
result += `${day}/${month}/${year.slice(2)} `;
}
console.log(result.trim());
What is the output?
Anonymous Quiz
34%
31/12/23 01/01/24
38%
2023-12-31 2024-01-01
16%
31/12/2023 01/01/2024
13%
31/12/23
CHALLENGE
function* counter() {
let count = 1;
while (true) {
const reset = yield count++;
if (reset) {
count = 1;
}
}
}
const gen = counter();
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next(true).value);
console.log(gen.next().value);CHALLENGE
function outer() {
console.log(typeof inner);
console.log(typeof inner2);
var inner = function() {
return 'Inside inner';
};
function inner2() {
return 'Inside inner2';
}
console.log(typeof inner);
console.log(typeof inner2);
}
outer();What’s New? — It’s that time of year again. The Ecma General Assembly has approved the ES2025 language specification, which you can read in full here if you have a gallon of coffee to hand — or you can enjoy Dr. Axel’s more succinct explainer instead.
Dr. Axel Rauschmayer
Please open Telegram to view this post
VIEW IN TELEGRAM
CHALLENGE
const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const result = numbers
.filter(num => num % 2 === 0)
.map(num => num * 2)
.reduce((acc, curr, idx, arr) => {
if (idx === arr.length - 1) {
return (acc + curr) / arr.length;
}
return acc + curr;
}, 0);
console.log(result);
Dr. Axel asks us to imagine if we had to write JavaScript without any whitespace or comments, so why should we have to write regexes that way? He has some tips for making the process more pleasant.
Dr. Axel Rauschmayer
Please open Telegram to view this post
VIEW IN TELEGRAM
CHALLENGE
const cache = new WeakMap();
const user1 = { name: 'Alice' };
const user2 = { name: 'Bob' };
cache.set(user1, { lastLogin: 'yesterday' });
cache.set(user2, { lastLogin: 'today' });
const result = [];
result.push(cache.has(user1));
result.push(cache.get(user2).lastLogin);
let user3 = { name: 'Charlie' };
cache.set(user3, { lastLogin: 'now' });
result.push(cache.has(user3));
user3 = null; // Removing the reference
// Garbage collector might run here in real situations
const user4 = { name: 'Charlie' }; // Same name, different object
result.push(cache.has(user4));
console.log(result);
What is the output?
Anonymous Quiz
22%
[false, 'today', true, false]
50%
[true, 'today', true, false]
9%
[true, undefined, true, false]
19%
[true, 'today', true, true]
HTML Embed Code: