JavaScript Code Checker
Lint JavaScript in your browser: ==, var, eval, innerHTML, debugger, console.log, unhandled promises and more. Free and private: runs in your browser.
Paste JavaScript to get ESLint-style findings with line numbers, plus complexity and empty-catch checks.
Runs entirely in your browser. Nothing you paste is uploaded or stored.
Use cases
- Check a function before opening a pull request.
- Explain a review comment with numbers instead of opinions.
- Find the riskiest code to refactor first.
Frequently asked questions
Why use === instead of ==?
== converts types before comparing, so "0" == 0 and null == undefined are true. === compares type and value and avoids those surprises.
Is the JavaScript Code Checker free?
Yes. It is free with no sign-up, and it runs entirely in your browser, so your input is never uploaded or stored.
How accurate is a browser-based code check?
It uses fast heuristics on the snippet you paste, so it is great for quick feedback. For whole repositories, cross-file analysis and history, run a full CodeInspector scan.
Related tools
Checking one snippet is a start. Scan your whole repository for free with CodeInspector.