JavaScript Tester

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Write and run JavaScript instantly in a safe sandbox — see console output, return values, errors and timing without opening DevTools. Free and runs in your browser.

Runs in a sandboxed iframe in your browser — nothing is sent to a server.

Press Ctrl/⌘ + Enter to run
JavaScript 
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Console
>_ Console output appears here

About JavaScript Tester

The JavaScript Tester is an online JS playground where you can write and run JavaScript instantly without opening DevTools or setting up a project. Type code in the editor, press Run or Ctrl/Cmd + Enter, and the console pane shows your log output, warnings, errors and execution time.

Your code executes inside a sandboxed iframe with no access to the surrounding page. Every run starts in a fresh sandbox, so leftover variables and runaway code from a previous attempt never pollute the next one, and blocking dialogs like alert are neutralized so the page never freezes.

Because everything runs client-side in your browser, nothing you type is sent to a server. It is a quick, private way to test a snippet from Stack Overflow, check async/await behavior, or debug a small function.

How to use JavaScript Tester

  1. Type or paste JavaScript into the editor pane, or click Sample for a working example.
  2. Click Run, or press Ctrl/Cmd + Enter, to execute the code.
  3. Read console.log, info, warn and error output — plus any thrown errors — in the console pane, with the execution time shown when the run finishes.
  4. Enable Auto-run to re-execute the code automatically as you edit.
  5. Use Clear console to empty the output, or Clear to start over with new code.

Frequently asked questions

Your script runs inside an iframe with the sandbox="allow-scripts" restriction, isolated from the page. Console output and errors are forwarded back for display, and the iframe is recreated on every run so previous state is discarded.

Calls to console.log, console.info, console.warn and console.error all appear in the console pane, along with uncaught errors and a timing line showing how many milliseconds the run took.

Yes. Modern syntax including async/await, promises, arrow functions and template literals runs exactly as it would in your browser, since the sandbox uses the same JavaScript engine as the page.

No. Everything executes locally in a sandboxed iframe in your browser; no code or output is transmitted to a server.

Yes. It is free, requires no sign-up, and you can run as many snippets as you like.
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