JavaScript online compiler

What runs your code

Good to know

• Runs on Node.js 24, the LTS release, with node code.js. require() and import both work. Top-level await works too, but not in a file that uses require(): use import there.
• Read all of the Input tab with require("fs").readFileSync(0, "utf8"), or line by line with readline.
• npm packages can't be installed, as there is no network.

Run JavaScript from your own code

Send the code and its input to the sync endpoint with an API key, and the output comes back in the response. The API docs cover the async endpoint with callbacks and every response field.

curl -X POST https://api.onlinecompiler.io/api/run-code-sync/ \
  -H "Authorization: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "compiler": "nodejs-24",
    "code": "const name = require(\"fs\").readFileSync(0, \"utf8\").trim();\nconsole.log(`Hello, ${name}!`);",
    "input": "Ada"
  }'

The response has output ("Hello, Ada!\n" here), error, exit_code, time and memory.

Put a runnable JavaScript example on your site

The editor above is the embeddable widget. Add the script and a div with your widget key, and your readers can edit and run the code without an account:

<script src="https://onlinecompiler.io/widget.js"></script>

<div class="runcode" data-key="YOUR_WIDGET_KEY" data-lang="nodejs-24">
  <script type="text/plain">
    const name = require("fs").readFileSync(0, "utf8").trim();
    console.log(`Hello, ${name}!`);
  </script>
</div>

On a platform that takes an iframe but not a script, such as many course sites, use the iframe embed. For Docusaurus, MkDocs, Sphinx and Mintlify, see runnable code examples in docs.

Other languages

Python, C, C++, Java, C#, F#, Go, Rust, PHP, Ruby, Haskell, TypeScript, SQL, Bash, Fortran, Visual Basic, Kotlin, R.

Frequently asked questions

Is this JavaScript online compiler free?

Yes. Running JavaScript on this page needs no account and shows no ads. To run JavaScript from your own app or site, the API and the widget are free up to 100,000 runs a month, commercial use included.

Can my JavaScript program read input?

Yes. Type it in the Input tab before you run, and the program reads it from standard input. The whole input is sent when you press Run, so a program can't ask for more while it runs.

Can I use JavaScript libraries?

Node.js's built-in modules, such as fs, readline and crypto. npm packages can't be installed, and programs have no network access.

How long can a program run?

Up to 30 seconds, with 512 MB of memory and 2 CPUs. A program still running at 30 seconds is stopped with exit code 124, and output over 64 KB per stream is cut.

Where does my code run?

On our servers, in a fresh gVisor sandbox with no network access that is deleted when the run ends. Each run is kept in execution history with its output; the security page says what is stored.