⚡ Online JavaScript Compiler
Write, run and test JavaScript right in your browser — full console output, smart autocomplete and async support. No setup, no sign-up, 100% private.
A JavaScript Playground in Your Browser
Everything you need to try an idea, test a snippet or learn the language — instantly and privately.
Instant Run
Write JS and run it immediately — full console output, no setup, no sign-up.
Async Ready
Promises, async/await and timers all work, logging output as they resolve.
Sandboxed & Safe
Code runs in an isolated worker with infinite-loop protection — the page never freezes.
Run Stats
See execution time, lines logged and error counts after every run.
Examples & Auto-Save
Start from built-in snippets; your code is saved locally between visits.
Light & Dark
A clean editor and console that follow your theme, right down to mobile.
How to Use the JavaScript Compiler
Four steps — write, run, read, repeat.
Write or paste code
Type JavaScript into the editor, or pick a ready-made example to start.
Press Run
Click ▶ Run or hit Ctrl/Cmd + Enter to execute it.
Read the console
console.log output appears directly below, with run-time and error stats.
Tweak & re-run
Each run starts fresh — edit and run again as often as you like.
Frequently Asked Questions
How to run code, async support, infinite-loop safety, the DOM, privacy, fresh state and timing.
How do I run JavaScript with this tool?
Type or paste your code into the editor, then press the ▶ Run button (or Ctrl/Cmd + Enter). Anything you log with console.log appears in the Console panel right below, along with the run time. There's nothing to install and no account needed — it works the moment the page loads.
Is this really a 'compiler'?
Strictly speaking, JavaScript isn't compiled ahead of time the way C++ is — it's run by an engine that compiles it just-in-time as it executes. 'Online JavaScript compiler' is simply the phrase most people search for when they want to run JS in the browser, which is exactly what this does. Under the hood it executes your code in a sandboxed Web Worker.
Does it support async/await and Promises?
Yes. Asynchronous code runs normally, and output appears in the console as each part resolves — so a setTimeout or an await will log at the right moment, not all at once. Try the 'Async / await' example to see it in action.
What happens if I write an infinite loop?
Nothing breaks. Your code runs in a separate worker thread, isolated from the page, and there's a built-in time limit — if execution runs too long it's stopped automatically and you're told it may be an infinite loop. You can also hit Stop at any time. The page itself never freezes.
Can I use the DOM, document or window?
Not in this sandbox. Because the code runs in a Web Worker for safety and isolation, there's no document or page DOM to manipulate — it's built for logic, algorithms, data and console output rather than building a webpage. Standard JavaScript, the full language, Math, JSON, Date, fetch, timers and so on all work.
Is my code uploaded or saved anywhere?
No. Everything runs entirely in your browser — your code is never sent to a server. It's auto-saved locally in your own browser storage so it's still there when you come back, and you can clear it any time with Reset.
Why is my variable 'already declared' error gone on the next run?
Each Run starts a brand-new sandbox, so variables and state from the previous run are wiped. That means you can re-run code with const and let declarations as many times as you like without 'already declared' errors piling up.
Can I see how long my code took to run?
Yes — after each run the Console header shows the execution time in milliseconds, plus how many lines were logged and how many errors occurred. It's a quick way to compare two approaches to the same problem.