π5β€3π₯1π€1
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();π4β€1
What is the output?
Anonymous Quiz
30%
function function function function
36%
undefined undefined function function
13%
function undefined function function
22%
undefined function function function
π5π₯3β€2π€1
Whatβs New? β Itβs 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 β or you can enjoy Dr. Axelβs more succinct explainer instead.
Dr. Axel Rauschmayer
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β€7π3π₯2π€1
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);
β€8π1
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
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β€7π€3π₯2π1
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);
β€5
What is the output?
Anonymous Quiz
24%
[false, 'today', true, false]
40%
[true, 'today', true, false]
17%
[true, undefined, true, false]
19%
[true, 'today', true, true]
π9π₯3β€1
CHALLENGE
const items = ['apple', 'banana', 'cherry', 'date'];
const result = items
.map(item => item.toUpperCase())
.filter(item => item.length > 5)
.reduce((acc, item, index) => {
return acc + (index === 0 ? '' : '-') + item.slice(0, 3);
}, '');
console.log(result);
β€2π₯1
What is the output?
Anonymous Quiz
27%
BANANA-CHERRY-DATE
44%
BAN-CHE
20%
BANANA-CHERRY
8%
BAN-CHE-DAT
π₯9π€2β€1
Hono is a framework well worth exploring. Itβs fast, lightweight, built on Web Standards, and can be used to build apps that work on numerous platforms from Node or Bun to Cloudflare or Fastly. v4.8 adds new route helper functions, improvements to JSX streaming and CORS, a new plugin system for static site generation, and more.
Yusuke Wada and Contributors
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β€7π1π₯1
CHALLENGE
const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const result = numbers
.filter(n => n % 2 === 0)
.map(n => n * 2)
.reduce((acc, curr, idx, arr) => {
if (idx === arr.length - 1) {
return (acc + curr) / arr.length;
}
return acc + curr;
}, 0);
console.log(result);
β€3π₯2π€2
π€8π€£3β€2π₯1
CHALLENGE
const teams = [
{ name: 'Warriors', players: ['Curry', 'Thompson'] },
{ name: 'Lakers', players: ['James', 'Davis'] }
];
const newTeams = JSON.parse(JSON.stringify(teams));
newTeams[0].players.push('Green');
const shallowCopy = [...teams];
shallowCopy[1].name = 'Clippers';
const freezeTest = Object.freeze({nested: {value: 42}});
freezeTest.nested.value = 100;
console.log(teams[1].name, teams[0].players.length, freezeTest.nested.value);
β€6π€£4
What is the output?
Anonymous Quiz
43%
Clippers 2 100
25%
Lakers 2 100
21%
Lakers 3 42
11%
Clippers 3 100
β€3π3π₯3
CHALLENGE
let x = 5;
function foo() {
console.log(x);
let x = 10;
console.log(x);
}
foo();
β€1
What is the output?
Anonymous Quiz
25%
ReferenceError: Cannot access 'x' before initialization
25%
undefined 10
14%
5 ReferenceError: x is not defined
36%
5 10
β€8π4π€£4π₯2
Deno 2.4 reintroduces the deno bundle command for creating single-file bundles for both the server and client side, complete with support for npm and JSR dependencies and automatic tree-shaking. You can also now include arbitrary files into modules using import, and Denoβs built-in OpenTelemetry support is now stable. Itβs a substantial release.
IwaΕczuk and Jiang
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β€3π2π₯1
CHALLENGE
const fruits = ['apple', 'banana', 'cherry'];
const newFruits = [...fruits];
newFruits.push('date');
const user = { name: 'Taylor', age: 30 };
const updatedUser = { ...user, age: 31 };
user.city = 'Seattle';
console.log(fruits.length, newFruits.length, user.city, updatedUser.city);
β€4