Online JavaScript Compiler & Playground

Your JavaScript runs in a Web Workerin your own browser, using the browser's native engine. There's no server round-trip: press Run and your device executes the code. console.log calls are captured and streamed to the output panel, and the final expression value is printed too.

For safety the sandbox is locked down before your code runs: there's no DOM, and network APIs (fetch, XMLHttpRequest, WebSocket) are disabled. So a snippet can compute and print, but it cannot make requests, touch our servers, or affect any other user — it's a pure, isolated scratchpad.

A 15-second timeout plus worker isolation means an accidental infinite loop is killed automatically without freezing your tab. Your code is wrapped in an async function, so top-level await just works.

• MDN — JavaScript reference and guides
• ECMA-262 — the JavaScript language specification

Execution uses your browser's built-in JavaScript engine inside a Web Worker; no third-party runtime is downloaded.