ESLint v2.0.0-beta.2 released

We just pushed ESLint v2.0.0-beta.2, which is a preview release upgrade of ESLint. As such, we have duplicated some of the content from the previous blog posts to make it easier to understand the differences between v1.10.3 and this version.

Note: This version of ESLint is not ready for production use and is provided to gather feedback from the community before releasing the final version. Please let us know if you having any problems or feedback by creating issues.


This is a summary of the major changes you need to know about for this version of ESLint.


Since this is a pre-release version, you will not automatically be upgraded by npm. You must specify the next tag when installing:

npm i eslint@next --save-dev

You can also specify the version directly:

npm i eslint@2.0.0-beta.2 --save-dev

Migration Guide

As there are a lot of changes, we’ve created a migration guide describing the changes in great detail along with the steps you should take to address them. Not all ESLint users will be affected by the changes, however, the changes are big enough that we recommend everyone read the migration thoroughly.

Code Path Analysis

ESLint v2.0.0 formally introduces code path analysis. While we’ve tried to make best guesses at how execution flowed through code, there were several instances where we just couldn’t get everything correct. For instance, trying to guarantee that every code path contained a return statement. Fully implementing code path analysis means that we (and you, through custom rules) can now correctly understand how execution is proceeding through code. Several rules have been updated to make use of code path analysis, fixing some longtime bugs in existing rules. As a result, ESLint is even better at picking up certain types of errors.

Configuration Cascading Changes

Prior to 2.0.0, if a directory contained both an .eslintrc file and a package.json file with ESLint configuration information, the settings from the two files would be merged together. In 2.0.0, only the settings from the .eslintrc.* file are used and the ones in package.json are ignored when both are present. Otherwise, package.json can still be used with ESLint configuration, but only if no other .eslintrc.* files are present.

Read more in the migration guide.

Language Options

Prior to 2.0.0, the way to enable language options was by using ecmaFeatures in your configuration. In 2.0.0:

  • The ecmaFeatures property is now under a top-level parserOptions property.
  • All ECMAScript 6 ecmaFeatures flags have been removed in favor of a ecmaVersion property under parserOptions that can be set to 3, 5 (default), or 6.
  • The ecmaFeatures.modules flag has been replaced by a sourceType property under parserOptions which can be set to "script" (default) or "module" for ES6 modules.

Read more in the migration guide.

Plugin Changes

This version of ESLint introduces several changes to plugins:

  1. rulesConfig is no longer supported. We had received complaints from users who didn’t know that plugins could automatically turn on certain rules, and that functionality doesn’t make sense because ESLint rules are supposed to be off by default. As such, rulesConfig will no longer set rules to be on or off by default.
  2. Plugins can now include environments. Environments are used to group global variables and parser options together, and now plugins can define custom environments.

Unicode BOM Support

If your files use a Unicode BOM, ESLint now properly handles parsing and evaluating your code and won’t get confused by its presence.

Built-In Global Variables

Prior to 2.0.0, new global variables that were standardized as part of ES6 such as Promise, Map, Set, and Symbol were included in the built-in global environment. This could lead to potential issues when, for example, no-undef permitted use of the Promise constructor even in ES5 code where promises are unavailable. In 2.0.0, the built-in environment only includes the standard ES5 global variables, and the new ES6 global variables have been moved to the es6 environment.

Read more in the migration guide.

Removing no-arrow-condition, Adding no-confusing-arrow

In looking at our rules, we discovered that no-arrow-condition actually overlapped with no-constant-condition, so we have removed no-arrow-condition as a core rule. The no-constant-condition will pick up the same errors as no-arrow-condition.

There was an additional condition that had been part of no-arrow-condition incorrectly, which checked for the use of arrow functions in conditional expressions. This functionality is now in the no-confusing-arrow rule.

New Visual Studio Formatter

We’ve added a new formatter called visualstudio, which formats the results into a format that Visual Studio understands. If you use Visual Studio with ESLint, this new formatter makes the console output interactive, so you can click on a warning and be taken straight to the location in the file.

New Rules

There are several new rules for this release:

Breaking Changes (v2.0.0-beta.2)

  • b28a19d Breaking: Plugins envs and config removal (fixes #4782, fixes #4952) (Nicholas C. Zakas)
  • 3e6a24e Breaking: Change strict default mode to “safe” (fixes #4961) (alberto)
  • 5b96265 Breaking: Update eslint:recommended (fixes #4953) (alberto)
  • 12fe803 Breaking: Supports Unicode BOM (fixes #4878) (Toru Nagashima)

Breaking Changes (v2.0.0-beta.1)

  • 19a9fbb Breaking: space-before-blocks ignores after keywords (fixes #1338) (Toru Nagashima)
  • b795850 Breaking: don’t load ~/.eslintrc when using --config flag (fixes #4881) (alberto)
  • e2f2b66 Breaking: Remove defaults from eslint:recommended (fixes #4809) (Ian VanSchooten)
  • d43f26c Breaking: migrate from minimatch to node-ignore (fixes #2365) (Stefan Grönke)
  • c07ca39 Breaking: merges keyword spacing rules (fixes #3869) (Toru Nagashima)

Breaking Changes (v2.0.0-alpha-2)

  • Breaking: deprecate no-arrow-condition rule (fixes #4417) (Luke Karrys)

Breaking Changes (v2.0.0-alpha-1)

  • Breaking: Correct links between variables and references (fixes #4615) (Toru Nagashima)
  • Breaking: Implement parserOptions (fixes #4641) (Nicholas C. Zakas)
  • Breaking: Remove space-after-keyword newline check (fixes #4149) (Nicholas C. Zakas)
  • Breaking: Treat package.json like the rest of configs (fixes #4451) (Ilya Volodin)
  • Breaking: Remove autofix from eqeqeq (fixes #4578) (Ilya Volodin)
  • Breaking: Remove ES6 global variables from builtins (fixes #4085) (Brandon Mills)
  • Breaking: Simplify rule schemas (fixes #3625) (Nicholas C. Zakas)
  • Breaking: added bower_components to default ignore (fixes #3550) (Julian Laval)
  • Breaking: Switch to Espree 3.0.0 (fixes #4334) (Nicholas C. Zakas)
  • Breaking: Freeze context object (fixes #4495) (Nicholas C. Zakas)
  • Breaking: Remove warnings of readonly from no-undef (fixes #4504) (Toru Nagashima)
  • Breaking: Implement yield-star-spacing rule (fixes #4115) (Bryan Smith)
  • Breaking: Default no-magic-numbers to none. (fixes #4193) (alberto)
  • Breaking: Allow empty arrow body (fixes #4411) (alberto)

Features (v2.0.0-beta.2)

  • 29392f8 New: allow-multiline option on comma-dangle (fixes #4967) (Alberto Gimeno)
  • 8470474 New: Add metadata to few test rules (fixes #4494) (Ilya Volodin)
  • 5e4841e New: ‘id-blacklist’ rule (fixes #3358) (Keith Cirkel)
  • bbf7f27 New: provide config.parser via parserName on RuleContext (fixes #3670) (Ben Mosher)

Features (v2.0.0-beta.1)

  • #d5c9435 New: ‘sort-imports’ rule (refs #3143) (Christian Schuller)
  • ceaf324 New: Add no-new-symbol rule (fixes #4862) (alberto)
  • 4665256 New: Add no-whitespace-before-property rule (fixes #1086) (Kai Cataldo)
  • 5ab564e New: ‘ignoreArrayIndexes’ option for ‘no-magic-numbers’ (fixes #4370) (Christian Schuller)
  • 97cdb95 New: Add no-useless-constructor rule (fixes #4785) (alberto)

Features (v2.0.0-alpha-2)

  • New: no-unmodified-loop-condition rule (fixes #4523) (Toru Nagashima)
  • New: Add a comment length option to the max-len rule (fixes #4665) (Ian)
  • New: Add greasemonkey environment (fixes #4715) (silverwind)
  • New: Add no-confusing-arrow rule (refs #4417) (Luke Karrys)
  • New: Visual Studio compatible formatter (fixes #4708) (rhpijnacker)

Features (v2.0.0-alpha-1)

  • New: Add no-implicit-globals rule (fixes #4542) (Joshua Peek)
  • New: array-callback-return rule (fixes #1128) (Toru Nagashima)
  • New: Add no-restricted-imports rule (fixes #3196) (Guy Ellis)
  • New: prefer-rest-params rule (fixes #4108) (Toru Nagashima)
  • New: Code Path Analysis (fixes #3530) (Toru Nagashima)

Enhancements (v2.0.0-beta.2)

  • 2b33c74 Update: valid-jsdoc to not require @return in constructors (fixes #4976) (Maga D. Zandaqo)
  • 05b8cb3 Update: Module overrides all ‘strict’ rule options (fixes #4936) (Nick Evans)
  • e0a9024 Update: Report newline between template tag and literal (fixes #4210) (Rajendra Patil)
  • da3336c Update: Rules should get sourceType from Program node (fixes #4960) (Nick Evans)
  • a2ac359 Update: Make jsx-quotes fixable (refs #4377) (Gabriele Petronella)
  • 700b8bc Update: Add “allow” option to allow specific operators (fixes #3308) (Rajendra Patil)
  • d82eeb1 Update: Add describe around rule tester blocks (fixes #4907) (Ilya Volodin)
  • 2967402 Update: Add minimum value to integer values in schema (fixes #4941) (Ilya Volodin)
  • b1360da Update: Support multiLine and singleLine options (fixes #4697) (Rajendra Patil)
  • d487013 Update: Option to allow extra parens for cond assign (fixes #3317) (alberto)
  • c2dee27 Update: Add module tests to no-extra-semi (fixes #4915) (Nicholas C. Zakas)
  • 5a633bf Update: Add preferType option to valid-jsdoc rule (fixes #3056) (Gyandeep Singh)

Enhancements (v2.0.0-beta.1)

  • 186e8f0 Update: Ignore camelcase in object destructuring (fixes #3185) (alberto)
  • 1569695 Update: Adds default ‘that’ for consistent-this (fixes #4833) (alberto)
  • 82d4cd9 Update: Add atomtest env (fixes #4848) (Andres Suarez)
  • 9c9beb5 Update: Add “ignore” override for operator-linebreak (fixes #4294) (Rajendra Patil)
  • 9c03abc Update: Add “allowCall” option (fixes #4011) (Rajendra Patil)
  • 1288ba4 Update: Add default limit to complexity (fixes #4808) (Ian VanSchooten)
  • 5050768 Update: Ask for commonjs under config init (fixes #3553) (Gyandeep Singh)
  • 9ea6b36 Update: Ignore case in jsdoc tags (fixes #4576) (alberto)
  • 4931f56 Update: optionally allow bitwise operators (fixes #4742) (Swaagie)

Enhancements (v2.0.0-alpha-2)

  • Update: Add “safe” mode to strict (fixes #3306) (Brandon Mills)
  • Update: Add cwd option for cli-engine (fixes #4472) (Ilya Volodin)
  • Update: Allow to omit semi for one-line blocks (fixes #4385) (alberto)
  • Update: configuration for classes in space-before-blocks (fixes #4089) (alberto)
  • Update: Implement auto fix for semi-spacing rule (fixes #3829) (alberto)
  • Update: option to ignore top-level max statements (fixes #4309) (alberto)

Enhancements (v2.0.0-alpha-1)

  • Update: no-use-before-define checks invalid initializer (fixes #4280) (Toru Nagashima)
  • Update: Add class body support to indent rule (fixes #4372) (Gyandeep Singh)
  • Update: Add ‘method’ option to no-empty (fixes #4605) (Kai Cataldo)
  • Update: Option to ignore constructor Fns object-shorthand (fixes #4487) (Kai Cataldo)
  • Update: add class option to no-use-before-define (fixes #3944) (Toru Nagashima)
  • Update: allowAfterThis option in no-underscore-dangle (fixes #3435) (just-boris)
  • Update: prefer-const begins to cover separating init (fixes #4474) (Toru Nagashima)

Bug Fixes (v2.0.0-beta.2)

  • b8fbaa0 Fix: multiple message in TAP formatter (fixes #4975) (Simon Degraeve)
  • 990f8da Fix: getNodeByRangeIndex performance issue (fixes #4989) (Toru Nagashima)
  • 5cd5429 Fix: function expression doc in call expression (fixes #4964) (Tim Schaub)
  • 4173baa Fix: no-dupe-class-members false positive (fixes #4981) (Toru Nagashima)
  • ee1014d Fix: Incorrect error location for object-curly-spacing (fixes #4957) (alberto)
  • b52ed17 Fix: Incorrect error location for space-in-parens (fixes #4956) (alberto)
  • 9c1bafb Fix: Columns of parse errors are off by 1 (fixes #4896) (alberto)
  • 86e6e57 Fix: Incorrect error at EOF for no-multiple-empty-lines (fixes #4917) (alberto)
  • 7f058f3 Fix: Incorrect location for padded-blocks (fixes #4913) (alberto)
  • b3de8f7 Fix: Do not show ignore messages for default ignored files (fixes #4931) (Gyandeep Singh)
  • 0f469b4 Fix: JSDoc for function expression on object property (fixes #4900) (Tim Schaub)
  • c4c4139 Fix: global-require no longer warns if require is shadowed (fixes #4812) (Kevin Partington)

Bug Fixes (v2.0.0-beta.1)

  • a8cfd56 Fix: remove duplicate of eslint-config-eslint (fixes #4909) (Toru Nagashima)
  • c275b41 Fix: no-extra-parens ExpressionStatement restricted prods (fixes #4902) (Michael Ficarra)
  • e5e06f8 Fix: Jsdoc comment for multi-line function expressions (fixes #4889) (Gyandeep Singh)
  • 7c9be60 Fix: Fix path errors in windows (fixes #4888) (Gyandeep Singh)
  • a1840e7 Fix: gray text was invisible on Solarized Dark theme (fixes #4886) (Jack Leigh)
  • 688f277 Fix: Set proper exit code for Node > 0.10 (fixes #4691) (Nicholas C. Zakas)
  • 58715e9 Fix: Use single quotes in messages (fixes #4845) (Joe Lencioni)
  • 5b7586b Fix: do not require a @return tag for @interface (fixes #4860) (Tim Schaub)
  • d3e8179 Fix: env is rewritten by modules (fixes #4814) (Toru Nagashima)
  • 315f272 Fix: Change max-warnings type to Int (fixes #4660) (George Zahariev)
  • f500d7d Fix: allow extending @scope/eslint/file (fixes #4800) (André Cruz)
  • b9bcbaf Fix: Bug in no-extra-bind (fixes #4806) (Andres Kalle)
  • acdda24 Fix: ignore argument parens in no-unexpected-multiline (fixes #4658) (alberto)

Bug Fixes (v2.0.0-alpha-2)

  • Fix: no-invalid-this allows this in static method (fixes #4669) (Toru Nagashima)
  • Fix: Add source property for fatal errors (fixes #3325) (Gyandeep Singh)
  • Fix: always-multiline for comma-dangle import (fixes #4704) (Nicholas C. Zakas)
  • Fix: Apply environment configs last (fixes #3915) (Nicholas C. Zakas)
  • Fix: Backtick behavior in quotes rule (fixes #3090) (Nicholas C. Zakas)
  • Fix: Check 1tbs non-block else (fixes #4692) (Nicholas C. Zakas)
  • Fix: Comma first issue in indent (fixes #4739, fixes #3456) (Gyandeep Singh)
  • Fix: Empty schemas forbid any options (fixes #4789) (Brandon Mills)
  • Fix: ensure ConfigOps.merge do a deep copy (fixes #4682) (Toru Nagashima)
  • Fix: Export class syntax for require-jsdoc rule (fixes #4667) (Gyandeep Singh)
  • Fix: Handle getters and setters in key-spacing (fixes #4792) (Brandon Mills)
  • Fix: no-constant-condition false positive (fixes #4737) (alberto)
  • Fix: ObjectRestSpread throws error in key-spacing rule (fixes #4763) (Ziad El Khoury Hanna)
  • Fix: Remove isMarkedAsUsed function name (fixes #4783) (Gyandeep Singh)
  • Fix: Remove path analysis from debug log (fixes #4631) (Ilya Volodin)
  • Fix: RuleTester to show parsing errors (fixes #4779) (Nicholas C. Zakas)
  • Fix: Set null to property ruleId when fatal is true (fixes #4722) (Sébastien Règne)
  • Fix: small typos in code examples (Plusb Preco)
  • Fix: support arrow functions in no-return-assign (fixes #4743) (alberto)

Bug Fixes (v2.0.0-alpha-1)

  • Fix: Update rule tests for parser options (fixes #4673) (Nicholas C. Zakas)
  • Fix: max-len rule overestimates the width of some tabs (fixes #4661) (Nick Evans)
  • Fix: Use oneValuePerFlag for --ignore-pattern option (fixes #4507) (George Zahariev)
  • Fix: Handle forbidden LineTerminators in no-extra-parens (fixes #4229) (Brandon Mills)
  • Fix: Check YieldExpression argument in no-extra-parens (fixes #4608) (Brandon Mills)
  • Fix: Do not cache package.json (fixes #4611) (Spain)
  • Fix: consistent-return checks the last (refs #3530, fixes #3373) (Toru Nagashima)
  • Fix: no-unreachable with the code path (refs #3530, fixes #3939) (Toru Nagashima)
  • Fix: no-this-before-super with the code path analysis (refs #3530) (Toru Nagashima)
  • Fix: no-fallthrough with the code path analysis (refs #3530) (Toru Nagashima)
  • Fix: constructor-super with the code path analysis (refs #3530) (Toru Nagashima)
  • Fix: Adding options unit tests for --ignore-pattern (refs #4507) (Kevin Partington)
  • Fix: no-eval come to catch indirect eval (fixes #4399, fixes #4441) (Toru Nagashima)

Documentation (v2.0.0-beta.2)

  • 3fa834f Docs: Fix formatter links (fixes #5006) (Gyandeep Singh)
  • 54b1bc8 Docs: Fix link in (fixes #5026) (Nick Evans)
  • 69f149d Docs: language tweaks (Andres Kalle)
  • 6ac2e01 Docs: Fix description of exported comment (Mickael Jeanroy)
  • ba11c1b Docs: Add Algolia as sponsor to README (Nicholas C. Zakas)
  • a456077 Docs: newline-after-var doesn’t allow invalid options. (alberto)
  • 82fbe09 Docs: Small semantic issue in documentation example (fixes #4937) (Marcelo Zarate)
  • 13a4e30 Docs: Formatting inconsistencies (fixes #4912) (alberto)
  • 2d626a3 Docs: Fix typo in changelog (Nicholas C. Zakas)

Documentation (v2.0.0-beta.1)

  • 6390862 Docs: Fix missing footnote (Yoshiya Hinosawa)
  • fc9f528 Docs: Modify unnecessary flag docs in quote-props (Matija Marohnić)
  • 0b3c01e Docs: Specify default for func-style (fixes #4834) (Ian VanSchooten)
  • 008ea39 Docs: Document default for operator assignment (fixes #4835) (alberto)
  • b566f56 Docs: no-new-func typo (alberto)
  • f7b28b7 Docs: clarify requireReturn option for valid-jsdoc rule (fixes #4859) (Tim Schaub)
  • 29516f1 Docs: fix migration guide for no-arrow-condition rule (Peter Newnham)
  • 2ef7549 Docs: clarify remedy to some prefer-const errors (Turadg Aleahmad)
  • fd72aba Docs: Example fix for no-extra-parens rule (fixes #3527) (Gyandeep Singh)
  • 246a6d2 Docs: Documentation fix (Andres Kalle)

Documentation (v2.0.0-alpha-2)

  • Docs: Add license header to Working with Rules guide (Brandon Mills)
  • Docs: Add section on file extensions to user-guide/configuring (adam)
  • Docs: Escape underscores in no-path-concat (alberto)
  • Docs: fix typos, suggests (molee1905)
  • Docs: RuleTester doesn’t require any tests (fixes #4681) (alberto)
  • Docs: Typo in generator-star (alberto)
  • Docs: Typo in no-unexpected-multiline (fixes #4756) (alberto)
  • Docs: Typo in no-useless-concat (alberto)
  • Docs: Typos in space-before-keywords and space-unary-ops (fixes #4771) (alberto)

Documentation (v2.0.0-alpha-1)

  • Docs: writing mistake (molee1905)
  • Docs: no-extra-semi no longer refers to deprecated rule (fixes #4598) (Kevin Partington)
  • Docs: Update docs/rules/ (Xiangyun Chi)
  • Docs: Add Code of Conduct (fixes #3095) (Nicholas C. Zakas)

Dependency Upgrades (v2.0.0-beta.2)

  • e0c5cf7 Upgrade: Espree to 3.0.0 (fixes #5018) (Ilya Volodin)
  • 7457a4e Upgrade: glob to 6.x (fixes #4991) (Gyandeep Singh)
  • 7b632f8 Upgrade: Globals to ^8.18.0 (fixes #4728) (Gyandeep Singh)

Dependency Upgrades (v2.0.0-beta.1)

  • 7c97201 Upgrade: doctrine version to 1.1.0 (fixes #4854) (Tim Schaub)
  • 871f534 Upgrade: Optionator version to 0.8.1 (fixes #4851) (Eric Johnson)

Dependency Upgrades (v2.0.0-alpha-2)

  • Upgrade: beefy to ^2.0.0, fixes installation errors (fixes #4760) (Kai Cataldo)

Dependency Upgrades (v2.0.0-alpha-1)

  • Upgrade: Handlebars to >= 4.0.5 for security reasons (fixes #4642) (Jacques Favreau)
  • d3f4bdd Build: Cleanup for code coverage (fixes #4983) (Gyandeep Singh)
  • 8ac1dac Build: Update markdownlint dependency to 0.1.0 (fixes #4988) (David Anson)
  • 1fc80e9 Build: Increment eslint-config-eslint (Nicholas C. Zakas)
  • ebd01b7 Build: Fix version number on release (fixes #4921) (Nicholas C. Zakas)
  • 6c70d84 Build: Fix prerelease script (fixes #4919) (Nicholas C. Zakas)
  • 3906481 Build: Add AppVeyor CI (fixes #4894) (Gyandeep Singh)
  • 407f329 Build: Fix prerelease script (Nicholas C. Zakas)
  • Build: Add prerelease script (Nicholas C. Zakas)
  • Build: Consume no-underscore-dangle allowAfterThis option (fixes #4599) (Kevin Partington)

The latest ESLint news, case studies, tutorials, and resources.

ESLint v9.7.0 released
1 min read

ESLint v9.7.0 released

We just pushed ESLint v9.7.0, which is a minor release upgrade of ESLint. This release adds some new features and fixes several bugs found in the previous release.

What's coming next for ESLint
5 min read

What's coming next for ESLint

The new configuration system is just the beginning of significant changes coming to ESLint.

ESLint v9.6.0 released
2 min read

ESLint v9.6.0 released

We just pushed ESLint v9.6.0, which is a minor release upgrade of ESLint. This release adds some new features and fixes several bugs found in the previous release.