What the JavaScript playground does
Type or paste JavaScript, run it, and see the output — console.log calls, return values and errors — in a panel beside the code. No project setup, no Node install, no signing in. It is the fastest way to test a regular expression, check how an array method behaves, try a snippet from documentation, or reproduce a bug in isolation. The code runs in your browser's JavaScript engine; nothing is sent to a server.
What you can use
| Available | Not available |
|---|---|
| All of modern JavaScript (ES2024): classes, async/await, destructuring, optional chaining, BigInt, Intl | Node.js APIs — require, fs, process, Buffer |
| Browser globals — fetch, setTimeout, JSON, Math, Date, crypto, localStorage | npm packages — no import from node_modules |
| console.log / warn / error / table, shown in the output panel | DOM of the page — the code runs in isolation from the tool's own UI |
| Errors with line numbers | Persistent state — everything resets on each run |
Example: things it is good for
// Check a regex
console.log("2026-06-14".match(/(\d{4})-(\d{2})-(\d{2})/).slice(1));
// Explore an array method
console.log([3, 1, 2].toSorted()); // [1, 2, 3] — original untouched
// Date and Intl behaviour
console.log(new Intl.NumberFormat("de-DE", { style: "currency", currency: "EUR" }).format(1234.5));
// Async
const r = await fetch("https://api.github.com/zen");
console.log(await r.text());Top-level await works, so you can call fetch against public APIs directly (subject to CORS). console.table renders arrays of objects as a grid.
Playground vs the browser console
- The console evaluates one line at a time; the playground runs a whole script and keeps it visible for editing and re-running.
- The console runs in the context of the current page (its DOM and globals); the playground runs isolated, which is cleaner for pure logic.
- The playground shows all output together, which is easier to read for loops and async sequences.
- For DOM work, use the Real-Time HTML Editor, which pairs HTML, CSS and JavaScript with a live preview.
Common uses
- Testing a regular expression against sample strings before putting it in production.
- Checking edge cases: what
parseInt("08")or[] + {}returns. - Prototyping a data transformation on a pasted JSON sample.
- Learning — trying examples from MDN or a tutorial with immediate feedback.
- Reproducing a bug in a minimal snippet to attach to an issue.
- Quick calculations that are easier in code than in a calculator.
Safety
Code runs with the same permissions as any script on this page: it can make network requests and use browser storage. Do not paste and run code you do not understand from untrusted sources, and do not put real credentials in the editor. Infinite loops will freeze the tab — reload if that happens, and add a counter or a timeout when experimenting with while.