Where does the code execute?

In a sandboxed iframe (separate origin) inside your browser — it is sent to no server and cannot access this site's data.

Can I use npm packages or the DOM?

The environment is a clean browser sandbox with standard Web APIs; npm packages cannot be imported, and DOM operations act on the sandbox's blank document.

Will an infinite loop freeze the page?

The sandbox has an execution timeout that terminates runaway code automatically, leaving the main page unaffected.

JavaScript Online Runner

Free online JavaScript runner: run code in an isolated sandbox iframe with live console capture and timeout protection.

Privacy: all processing happens locally in your browser. Your input never leaves your device.

What is JavaScript Online Runner?

Verifying a piece of JS logic should not require Node or a new project: paste the code, hit run, and console.log output appears in real time. Code executes in a sandboxed iframe on a separate origin, fully isolated from the main page — it cannot read your cookies or page data — and all computation happens on your machine. Great for algorithm checks, API behavior tests and interview practice.

How to Use

Paste JavaScript code
Click Run (or press Ctrl+Enter)
View console output and the return value

FAQ

Where does the code execute?: In a sandboxed iframe (separate origin) inside your browser — it is sent to no server and cannot access this site's data.
Can I use npm packages or the DOM?: The environment is a clean browser sandbox with standard Web APIs; npm packages cannot be imported, and DOM operations act on the sandbox's blank document.
Will an infinite loop freeze the page?: The sandbox has an execution timeout that terminates runaway code automatically, leaving the main page unaffected.

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Last updated 2026-09-04