AST-based pattern checker for JavaScript

 ESLint is a tool for identifying and reporting on patterns
 found in ECMAScript/JavaScript code.
 In many ways, it is similar to JSLint and JSHint
 with a few exceptions:
 .
  * ESLint uses Espree for JavaScript parsing
  * ESLint uses an AST to evaluate patterns in code
  * ESLint is completely pluggable,
    every single rule is a plugin and you can add more at runtime
 .
 Some uses of ESLint require additional packages:
  * Use of parsers other than the default (Espree) require that parser,
    e.g. node-babel-eslint, node-esprima, or node-esprima-fb.
  * Output format "code-frame" requires node-babel-code-frame.
  * Output format "table" requires node-table and node-pluralize.