Master JavaScript with interactive interview questions. Execute code in-browser, visualize the event loop, and commit the mechanics to memory. A precision instrument for interview prep.
Built by @kitsunekode. Based on Lydia Hallie's questions.
function getAge() {
'use strict';
age = 21;
console.log(age);
}
getAge();Coming Soon
Build real components, explore patterns, and master React — with a live Sandpack IDE inside every challenge.
Build real components with a live Sandpack IDE. No config, no boilerplate — just React and you.
function Counter() { const [count, setCount] = useState(0); return ( <button onClick={() => setCount(c => c+1)} > Clicked {count} times </button> ) }
The Practice Loop
Patterns
From Lydia Hallie's javascript-react-patterns — distilled into interactive challenges.
How it works
A precision-engineered feedback cycle designed to commit advanced JavaScript to your long-term memory.
Filter by topic, dial in the difficulty, or search directly to a concept.
No peeking. Force yourself to commit before the explanation reveals.
Pop open the scratchpad. Execute snippets. See raw output immediately.
Deep dive into the explanation. Deconstruct the event loop and execution context.
Coverage
Comprehensive coverage across 9 core topics
82 challenges
48 challenges
39 challenges
21 challenges
17 challenges
17 challenges
15 challenges
13 challenges
7 challenges
Start with these popular challenges
function sayHi() { console.log(name); console.log(age);for (var i = 0; i < 3; i++) { setTimeout(() => console.log(i), 1);}const shape = { radius: 10, diameter() {+true;!'Lydia';const bird = { size: 'small',};let c = { greeting: 'Hey!' };let d;