JavaScript Runner
WebRun JavaScript in your browser with console output capture. The sandbox isolates execution from the page and keeps a history so you can rerun experiments.
Click "Run" to see output...
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About JavaScript Runner
Need a quick way to verify a JavaScript snippet without booting up an IDE or a Node project? This tool executes JavaScript directly in the browser, captures console.log/warn/error/info output, and reports execution time in milliseconds. It supports all modern ES6+ syntax — arrow functions, async/await, optional chaining, nullish coalescing, destructuring, and template literals — so you can test real snippets as you write them. Because it runs in a browser sandbox rather than Node.js, Node built-ins like require, fs, or process are unavailable, but the full set of browser Web APIs is at your disposal. You can define variables and functions in one step and reference them later, making it handy for incrementally debugging complex logic and verifying an array or string algorithm. Pasted code executes locally with nothing uploaded, ideal for learning, quick experiments, and sharing runnable examples in docs or forum answers. Two cautions: avoid running untrusted code, and avoid mutating the page's global state.
How to Use
- Open the JavaScript Runner tool
- Enter or paste the content to process
- Adjust the output options as needed
- Click the Run button; results appear in real time
- Copy or export the result
Use Cases
- Verify algorithms — Paste code snippets and see results and output immediately.
- Learn JavaScript — Practice while learning with real-time execution feedback.
- Debug regex — Quickly test regex match results without switching tools.
- Verify data processing — Test JSON parsing, array operations, and data processing code.
- Step-by-step debugging — Define variables and functions first, then reference them in later runs to validate complex logic.
- Share runnable snippets — Provide reproducible JS examples in docs or forum answers so others can run and confirm them.
FAQ
Is it safe?
Code runs via new Function in the browser, isolating the global scope. However, do not run untrusted code.
Does it support ES6+?
Yes. The browser natively supports all modern JavaScript syntax including async/await, arrow functions, destructuring, etc.
Can I use DOM APIs?
You can access document and window objects, but modifications may affect this page. Stick to pure logic.
Does it support Node.js APIs?
No. This is a browser environment without require, fs, process, or other Node.js APIs.
Can I run async code?
Yes. Write an async function and await inside it; results are captured and shown together, with millisecond timing for verification.
Are uncaught exceptions shown?
Yes. Thrown errors are caught and printed in red with a stack trace, making it easy to locate the failing line.