A complete toolkit for beginners and pros. Write, run, and understand JavaScript — with zero setup, zero friction, zero excuses.
From a beginner's first hello world to a senior dev prototyping a component — there's a tool for every moment.
Write JavaScript with syntax highlighting, auto-complete, and a live console. Supports ES2024 out of the box. Perfect for scripts, algorithms, and exploring APIs.
Like Jupyter — but for JavaScript. Run code cells one at a time, see output inline, and build up concepts step by step. Great for tutorials and experiments.
Write React components with JSX syntax and see them live in a split preview. No bundler setup, no config — just components that work immediately.
Write TypeScript and see it transpiled in real time. Understand type errors, interfaces, generics, and why TypeScript makes large codebases sane.
A full HTML/CSS/JS playground with a live preview pane. Build mini UIs, test DOM manipulation, or prototype a landing page concept instantly.
Paste raw JSON and get a beautiful, collapsible tree view with syntax validation, search, and formatting. Indispensable when debugging APIs.
Every concept is runnable. Switch between examples to see JavaScript patterns that actually matter.
console.log
output, errors, and warnings instantly as you type.// Variables, functions & closures const greet = (name) => { const hour = new Date().getHours(); const time = hour < 12 ? 'morning' : hour < 18 ? 'afternoon' : 'evening'; return `Good ${time}, ${name}!`; }; // Destructuring + default params const profile = ({ name = 'stranger', age }) => `${name} is ${age} years old`; console.log(greet('Ayesha')); console.log(profile({ name: 'Rohan', age: 24 }));
// Async/await with error handling const fetchUser = async (id) => { try { const res = await fetch( `https://api.example.com/users/${id}` ); if (!res.ok) throw new Error('Not found'); const { name, email } = await res.json(); return { name, email }; } catch (err) { console.error(`Error: ${err.message}`); } }; // Promise.all — run in parallel const users = await Promise.all( [1, 2, 3].map(fetchUser) );
// Array methods — map, filter, reduce const products = [ { name: 'Laptop', price: 999, inStock: true }, { name: 'Mouse', price: 49, inStock: false }, { name: 'Desk', price: 349, inStock: true }, ]; const total = products .filter(p => p.inStock) .map(p => p.price) .reduce((sum, p) => sum + p, 0); console.log(`Total: $${total}`); // Optional chaining + nullish coalescing const first = products[0]?.name ?? 'Unknown';
Finally a JS playground that doesn't feel like it was designed in 2012. The notebook mode is exactly what I needed to explain closures to my students.
I switched from CodePen because the TypeScript editor here actually shows me type errors in real time. Zero config, it just works.
As a self-taught developer, having everything in one clean tool kept me focused. I went from zero JS to my first job in 8 months.
The JSON viewer saved me hours of debugging a nasty API response. Clean tree view, instant validation — bookmark this immediately.
I run coding bootcamps and this is now our primary tool for live demos. Students can follow along without fighting with local environments.
The React editor is surprisingly capable. I built a full working counter app prototype to pitch to my team — no setup, no drama.
No download. No signup. Just open a tool and go.