Where does my JavaScript run?

Inside a Web Worker. The parent tab can terminate the worker on Stop or timeout, so an infinite loop cannot freeze the page. Console.log is captured into the Output panel.

No. Source stays in this tab and in localStorage on your device.

No. Workers have no document. For HTML/CSS/JS together use the HTML Editor, which live-previews a full page.

What happens on an infinite loop?

Run stops after a few seconds and reports a timeout so the tab stays usable.

JavaScript Playground

Write JavaScript, press Run, and read console output below. Everything stays in your browser.

Output appears here after Run.

About this tool

JavaScript Playground runs entirely in your browser on DevTools — no signup, no upload.

What this tool does not do

JavaScript Playground is a free in-browser utility, not a hosted API, and keeps no server-side history.

How to use this tool

Using JavaScript Playground
Open JavaScript Playground, enter or paste your input, and copy the result.

Bill Tracker

Track subscriptions, memberships and recurring bills on a private paid/skipped calendar.

Pill Tracker

Track supplements by meal, empty or with food, and mark taken or skipped on a private calendar.

TypeScript Playground

Compile TypeScript to JavaScript in your tab and inspect console output.

Dart Playground

Write Dart, press Run, and see print output in your browser.

Ruby Playground

Run Ruby in your browser with ruby.wasm. First Run downloads the VM, then caches it.

Numerology Analyzer

Life Path, Destiny, Soul Urge and Personality numbers from a birth name and date.