JSHint

JSHint is a community-driven static code analysis tool for JavaScript that scans programs and reports commonly made mistakes and potential bugs, including syntax errors, issues caused by implicit type conversion, and leaking variables. It is designed to help developers catch problems that may not surface when code is written, while remaining configurable to match the environment where the code will run. The project is publicly available under the MIT Expat license.

The tool provides configurable checks for cyclomatic complexity, unused and undefined variables, comparisons with null, debugging code, unsafe for..in loops, arguments.caller and .callee, assignments in if/for statements, functions inside loops, eval, unsafe line breaks, potential typos in logical operators, non-strict mode code, and new used for side-effects. It can assume Browser, NodeJS, jQuery, or development environments, and supports newer JavaScript features, Mozilla extensions, and older ES3 environments. JSHint can be used online or installed locally, with documentation, installation guidance, and contribution resources available. It is intended for JavaScript developers and teams, and is offered as a free, open-source tool rather than through paid editions or usage-based plans.