JavaScript Formatter & Tester

Format JavaScript with Monaco syntax highlighting, beautify or minify for delivery, validate structure, and execute code safely in a sandboxed iframe with console capture for logs, errors, return values, and execution time. Supports console.log, functions, loops, arrays, objects, promises, and async/await. Upload or paste .js files, adjust indentation, copy or download output, and replay from local history — all without sending your code to ToolsLibrary servers.

How to Use the JavaScript Formatter & Tester

Paste or upload JavaScript, choose formatting options, beautify or minify, validate syntax, or run code in the sandbox and read console output.

  1. Paste JavaScript into the input editor or upload a .js / .mjs / .cjs file.
  2. Set indentation (2 spaces, 4 spaces, or tabs) in the formatting options.
  3. Click Beautify to pretty-print, Minify to compress, or Validate to check syntax only.
  4. Review errors in the editor or statistics panel when a run fails.
  5. Click Run to execute the current input in the sandbox and inspect console logs, errors, and execution time.
  6. Copy or download formatted output, or reload a prior run from History.

Beautify vs minify vs validate vs run

  • Beautify — readable multi-line JavaScript with your chosen indent.
  • Minify — smallest whitespace-safe script for delivery.
  • Validate — syntax check only; formatting unchanged.
  • Run — executes in an isolated iframe and captures console output.

Worked example

Paste a short async snippet, click Run, and confirm console.log lines appear under Sandbox output along with execution time. Then click Beautify to produce a readable version for sharing.

Privacy

Formatting, validation, and sandbox runs stay in your browser. History entries may sync only when you are signed in and explicitly save — not by default.

Limitations

The sandbox does not provide Node.js APIs, npm imports, or unrestricted network access. Very large files may be limited by browser memory.

FAQ

Is code execution safe?

Yes. Code runs in a sandboxed iframe without same-origin access to the ToolsLibrary page. Network and DOM access to the parent page are blocked.

What is the difference between Beautify and Minify?

Beautify adds indentation and line breaks for readability. Minify removes unnecessary whitespace to produce a compact script suitable for delivery.

Does my JavaScript leave the browser?

Formatting, validation, and sandbox execution run locally in your browser. ToolsLibrary does not upload your source code unless you explicitly save history while signed in.

Can I run async/await and promises?

Yes. The sandbox supports async functions, Promise chains, and console output from asynchronous code. Execution time is shown after the run completes.

What does Validate do?

Validate checks JavaScript syntax without changing formatting. Use it when you want error feedback before beautifying or minifying.

Can I upload a .js file?

Yes. Use the file picker or drag-and-drop to load .js, .mjs, .cjs, or plain text files into the Monaco editor.

What appears in the sandbox output panel?

Console logs, runtime errors, the return value of the last expression (when available), and total execution time in milliseconds.

Which indentation options are available?

Choose 2 spaces, 4 spaces, or tabs in the formatting options. Your choice applies to Beautify output.

Can I copy or download formatted output?

Yes. After a successful Beautify or Minify run, copy from the output editor or download the result from the toolbar.

What are the sandbox limits?

The sandbox is for quick snippets and learning — not a full Node.js or browser DOM environment. Modules, fetch to arbitrary hosts, and parent-page APIs are not available inside the iframe.