Many JavaScript implementations do not warn against questionable coding
practices. Yes, that's nice for the site that "works best with Internet
Explorer" (designed with templates, scripted with snippets copied from
forums). But it's a nightmare when you actually want to write quality,
maintainable code.

That's where JavaScript Lint comes in. With JavaScript Lint, you can
check all your JavaScript source code for common mistakes without actually
running the script or opening the web page.

JavaScript Lint holds an advantage over competing lints because it is
based on the JavaScript engine for the Firefox browser. This provides
a robust framework that can not only check JavaScript syntax but also
examine the coding techniques used in the script and warn against
questionable practices.

WWW: http://www.javascriptlint.com/