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Input

Online JavaScript Playground

Runs on Node.js 12.14.0 · Free · No signup required

This is a free online JavaScript playground built for backend engineers. Write JavaScript, run it against a real Node.js runtime, and see the output immediately — no local install, no configuration, no signup. It is designed for the moment you want to check whether something actually works: a bit of async logic, an array method you half-remember, a quick algorithm sketch before you commit it to a real codebase. The editor supports standard input, so you can test programs that read from stdin the same way they would on a server. Everything runs server-side, so what you see here matches what Node would do in production rather than what a browser console would do. If you are learning backend JavaScript rather than just testing it, the playground pairs with our Node.js projects and courses.

JavaScript Playground — Frequently Asked Questions

Is this JavaScript playground free?
Yes. It is free to use and requires no account. Write code, hit run, and you get output.
Which Node.js version does it run?
Code executes server-side against a Node.js runtime, so language features and standard-library behaviour match a real server environment rather than a browser.
Can I pass input to my program?
Yes. The playground supports standard input, so programs that read from stdin behave exactly as they would when run from a terminal.

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Ready to build real backends rather than test snippets? Explore backend engineering courses and projects at MasteringBackend.