Report

Cyclomatic complexity Unused variables Undefined variables

Warn

About == null About debugging code About unsafe for..in About arguments.caller and .callee About assignments if/for/... About functions inside loops About eval About unsafe line breaks About potential typos in logical operators When code is not in strict mode When new is used for side-effects

Assume

Browser NodeJS jQuery Development (console, etc.) New JavaScript features (ES6) Mozilla JavaScript extensions Older environments (ES3)