Playground
Write anything. Run executes your code for real in the browser. Step replays it one top-level statement at a time using a simplified execution model — a lightweight approximation, not a full JS engine.
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Console
Output will appear here
Variables (step mode)
Use Step to see top-level variables as they're assigned
About this playground
- Run executes your exact code in a real JavaScript sandbox — async output (timers, promises) streams in naturally.
- Step re-runs your code one top-level statement further each time, so you can watch output and variables build up gradually.
- For a true instruction-by-instruction walkthrough with call stack and scope diagrams, see the curated lessons in the sidebar — closures and the event loop are good places to start.