ESLint

ESLint is a pluggable linting utility for JavaScript and TypeScript code, originally created by Nicholas C. Zakas in 2013. With over 25,200 stars as of 2026, ESLint is the most widely used JavaScript linter, integrated into virtually every modern JavaScript and TypeScript project. Unlike earlier linters like JSHint and JSLint, ESLint was designed from the ground up to be fully pluggable: every rule is a separate module, and users can mix and match rules, create custom rules, and share configurations. Key features include: 200+ built-in rules covering code quality (no-unused-vars, no-undef), best practices (no-eval, no-implied-eval, eqeqeq for strict equality), style preferences (indent, quotes, semi, comma-dangle), ECMAScript 6+ features (prefer-const, no-var, arrow-body-style), TypeScript-specific rules (via typescript-eslint parser and plugin), and React/Vue/Angular framework-specific rules (via community plugins), pluggable architecture allowing custom rules, formatters, and parsers, shareable configuration (predefined rule sets published as npm packages like eslint-config-airbnb, eslint-config-standard, eslint-config-prettier for integrating with Prettier), automatic fix capability (--fix flag) that automatically corrects fixable rule violations, configuration via .eslintrc files in JSON, YAML, JavaScript, or package.json, cascading configuration (parent directory configurations apply to child directories with overrides), per-file overrides (applying different rules to different file patterns), parser options for ECMAScript versions and source types (script vs module), environment definitions (browser, node, es2021, jest) for predefined globals, integration with all major editors (VS Code, WebStorm, Sublime, Vim, Emacs), and CI/CD integration via ESLint CLI and GitHub Actions.