eslint/README.md

   1 [![npm version](https://img.shields.io/npm/v/eslint.svg)](https://www.npmjs.com/package/eslint)
   2 [![Downloads](https://img.shields.io/npm/dm/eslint.svg)](https://www.npmjs.com/package/eslint)
   3 [![Build Status](https://github.com/eslint/eslint/workflows/CI/badge.svg)](https://github.com/eslint/eslint/actions)
   4 [![FOSSA Status](https://app.fossa.io/api/projects/git%2Bhttps%3A%2F%2Fgithub.com%2Feslint%2Feslint.svg?type=shield)](https://app.fossa.io/projects/git%2Bhttps%3A%2F%2Fgithub.com%2Feslint%2Feslint?ref=badge_shield)
   5 <br />
   6 [![Open Collective Backers](https://img.shields.io/opencollective/backers/eslint)](https://opencollective.com/eslint)
   7 [![Open Collective Sponsors](https://img.shields.io/opencollective/sponsors/eslint)](https://opencollective.com/eslint)
   8 [![Follow us on Twitter](https://img.shields.io/twitter/follow/geteslint?label=Follow&style=social)](https://twitter.com/intent/user?screen_name=geteslint)
   9
  10 # ESLint
  11
  12 [Website](https://eslint.org) |
  13 [Configuring](https://eslint.org/docs/user-guide/configuring) |
  14 [Rules](https://eslint.org/docs/rules/) |
  15 [Contributing](https://eslint.org/docs/developer-guide/contributing) |
  16 [Reporting Bugs](https://eslint.org/docs/developer-guide/contributing/reporting-bugs) |
  17 [Code of Conduct](https://js.foundation/community/code-of-conduct) |
  18 [Twitter](https://twitter.com/geteslint) |
  19 [Mailing List](https://groups.google.com/group/eslint) |
  20 [Chat Room](https://eslint.org/chat)
  21
  22 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:
  23
  24 * ESLint uses [Espree](https://github.com/eslint/espree) for JavaScript parsing.
  25 * ESLint uses an AST to evaluate patterns in code.
  26 * ESLint is completely pluggable, every single rule is a plugin and you can add more at runtime.
  27
  28 ## Table of Contents
  29
  30 1. [Installation and Usage](#installation-and-usage)
  31 2. [Configuration](#configuration)
  32 3. [Code of Conduct](#code-of-conduct)
  33 4. [Filing Issues](#filing-issues)
  34 5. [Frequently Asked Questions](#faq)
  35 6. [Releases](#releases)
  36 7. [Security Policy](#security-policy)
  37 8. [Semantic Versioning Policy](#semantic-versioning-policy)
  38 9. [License](#license)
  39 10. [Team](#team)
  40 11. [Sponsors](#sponsors)
  41 12. [Technology Sponsors](#technology-sponsors)
  42
  43 ## <a name="installation-and-usage"></a>Installation and Usage
  44
  45 Prerequisites: [Node.js](https://nodejs.org/) (`^10.12.0`, or `>=12.0.0`) built with SSL support. (If you are using an official Node.js distribution, SSL is always built in.)
  46
  47 You can install ESLint using npm:
  48
  49 ```
  50 $ npm install eslint --save-dev
  51 ```
  52
  53 You should then set up a configuration file:
  54
  55 ```
  56 $ ./node_modules/.bin/eslint --init
  57 ```
  58
  59 After that, you can run ESLint on any file or directory like this:
  60
  61 ```
  62 $ ./node_modules/.bin/eslint yourfile.js
  63 ```
  64
  65 ## <a name="configuration"></a>Configuration
  66
  67 After running `eslint --init`, you'll have a `.eslintrc` file in your directory. In it, you'll see some rules configured like this:
  68
  69 ```json
  70 {
  71     "rules": {
  72         "semi": ["error", "always"],
  73         "quotes": ["error", "double"]
  74     }
  75 }
  76 ```
  77
  78 The names `"semi"` and `"quotes"` are the names of [rules](https://eslint.org/docs/rules) in ESLint. The first value is the error level of the rule and can be one of these values:
  79
  80 * `"off"` or `0` - turn the rule off
  81 * `"warn"` or `1` - turn the rule on as a warning (doesn't affect exit code)
  82 * `"error"` or `2` - turn the rule on as an error (exit code will be 1)
  83
  84 The three error levels allow you fine-grained control over how ESLint applies rules (for more configuration options and details, see the [configuration docs](https://eslint.org/docs/user-guide/configuring)).
  85
  86 ## <a name="code-of-conduct"></a>Code of Conduct
  87
  88 ESLint adheres to the [JS Foundation Code of Conduct](https://js.foundation/community/code-of-conduct).
  89
  90 ## <a name="filing-issues"></a>Filing Issues
  91
  92 Before filing an issue, please be sure to read the guidelines for what you're reporting:
  93
  94 * [Bug Report](https://eslint.org/docs/developer-guide/contributing/reporting-bugs)
  95 * [Propose a New Rule](https://eslint.org/docs/developer-guide/contributing/new-rules)
  96 * [Proposing a Rule Change](https://eslint.org/docs/developer-guide/contributing/rule-changes)
  97 * [Request a Change](https://eslint.org/docs/developer-guide/contributing/changes)
  98
  99 ## <a name="faq"></a>Frequently Asked Questions
 100
 101 ### I'm using JSCS, should I migrate to ESLint?
 102
 103 Yes. [JSCS has reached end of life](https://eslint.org/blog/2016/07/jscs-end-of-life) and is no longer supported.
 104
 105 We have prepared a [migration guide](https://eslint.org/docs/user-guide/migrating-from-jscs) to help you convert your JSCS settings to an ESLint configuration.
 106
 107 We are now at or near 100% compatibility with JSCS. If you try ESLint and believe we are not yet compatible with a JSCS rule/configuration, please create an issue (mentioning that it is a JSCS compatibility issue) and we will evaluate it as per our normal process.
 108
 109 ### Does Prettier replace ESLint?
 110
 111 No, ESLint does both traditional linting (looking for problematic patterns) and style checking (enforcement of conventions). You can use ESLint for everything, or you can combine both using Prettier to format your code and ESLint to catch possible errors.
 112
 113 ### Why can't ESLint find my plugins?
 114
 115 * Make sure your plugins (and ESLint) are both in your project's `package.json` as devDependencies (or dependencies, if your project uses ESLint at runtime).
 116 * Make sure you have run `npm install` and all your dependencies are installed.
 117 * Make sure your plugins' peerDependencies have been installed as well. You can use `npm view eslint-plugin-myplugin peerDependencies` to see what peer dependencies `eslint-plugin-myplugin` has.
 118
 119 ### Does ESLint support JSX?
 120
 121 Yes, ESLint natively supports parsing JSX syntax (this must be enabled in [configuration](https://eslint.org/docs/user-guide/configuring)). Please note that supporting JSX syntax *is not* the same as supporting React. React applies specific semantics to JSX syntax that ESLint doesn't recognize. We recommend using [eslint-plugin-react](https://www.npmjs.com/package/eslint-plugin-react) if you are using React and want React semantics.
 122
 123 ### What ECMAScript versions does ESLint support?
 124
 125 ESLint has full support for ECMAScript 3, 5 (default), 2015, 2016, 2017, 2018, 2019, and 2020. You can set your desired ECMAScript syntax (and other settings, like global variables or your target environments) through [configuration](https://eslint.org/docs/user-guide/configuring).
 126
 127 ### What about experimental features?
 128
 129 ESLint's parser only officially supports the latest final ECMAScript standard. We will make changes to core rules in order to avoid crashes on stage 3 ECMAScript syntax proposals (as long as they are implemented using the correct experimental ESTree syntax). We may make changes to core rules to better work with language extensions (such as JSX, Flow, and TypeScript) on a case-by-case basis.
 130
 131 In other cases (including if rules need to warn on more or fewer cases due to new syntax, rather than just not crashing), we recommend you use other parsers and/or rule plugins. If you are using Babel, you can use the [babel-eslint](https://github.com/babel/babel-eslint) parser and [eslint-plugin-babel](https://github.com/babel/eslint-plugin-babel) to use any option available in Babel.
 132
 133 Once a language feature has been adopted into the ECMAScript standard (stage 4 according to the [TC39 process](https://tc39.github.io/process-document/)), we will accept issues and pull requests related to the new feature, subject to our [contributing guidelines](https://eslint.org/docs/developer-guide/contributing). Until then, please use the appropriate parser and plugin(s) for your experimental feature.
 134
 135 ### Where to ask for help?
 136
 137 Join our [Mailing List](https://groups.google.com/group/eslint) or [Chatroom](https://eslint.org/chat).
 138
 139 ## <a name="releases"></a>Releases
 140
 141 We have scheduled releases every two weeks on Friday or Saturday. You can follow a [release issue](https://github.com/eslint/eslint/issues?q=is%3Aopen+is%3Aissue+label%3Arelease) for updates about the scheduling of any particular release.
 142
 143 ## <a name="security-policy"></a>Security Policy
 144
 145 ESLint takes security seriously. We work hard to ensure that ESLint is safe for everyone and that security issues are addressed quickly and responsibly. Read the full [security policy](https://github.com/eslint/.github/blob/master/SECURITY.md).
 146
 147 ## <a name="semantic-versioning-policy"></a>Semantic Versioning Policy
 148
 149 ESLint follows [semantic versioning](https://semver.org). However, due to the nature of ESLint as a code quality tool, it's not always clear when a minor or major version bump occurs. To help clarify this for everyone, we've defined the following semantic versioning policy for ESLint:
 150
 151 * Patch release (intended to not break your lint build)
 152     * A bug fix in a rule that results in ESLint reporting fewer linting errors.
 153     * A bug fix to the CLI or core (including formatters).
 154     * Improvements to documentation.
 155     * Non-user-facing changes such as refactoring code, adding, deleting, or modifying tests, and increasing test coverage.
 156     * Re-releasing after a failed release (i.e., publishing a release that doesn't work for anyone).
 157 * Minor release (might break your lint build)
 158     * A bug fix in a rule that results in ESLint reporting more linting errors.
 159     * A new rule is created.
 160     * A new option to an existing rule that does not result in ESLint reporting more linting errors by default.
 161     * An existing rule is deprecated.
 162     * A new CLI capability is created.
 163     * New capabilities to the public API are added (new classes, new methods, new arguments to existing methods, etc.).
 164     * A new formatter is created.
 165     * `eslint:recommended` is updated and will result in strictly fewer linting errors (e.g., rule removals).
 166 * Major release (likely to break your lint build)
 167     * `eslint:recommended` is updated and may result in new linting errors (e.g., rule additions, most rule option updates).
 168     * A new option to an existing rule that results in ESLint reporting more linting errors by default.
 169     * An existing formatter is removed.
 170     * Part of the public API is removed or changed in an incompatible way. The public API includes:
 171         * Rule schemas
 172         * Configuration schema
 173         * Command-line options
 174         * Node.js API
 175         * Rule, formatter, parser, plugin APIs
 176
 177 According to our policy, any minor update may report more linting errors than the previous release (ex: from a bug fix). As such, we recommend using the tilde (`~`) in `package.json` e.g. `"eslint": "~3.1.0"` to guarantee the results of your builds.
 178
 179 ## <a name="license"></a>License
 180
 181 [![FOSSA Status](https://app.fossa.io/api/projects/git%2Bhttps%3A%2F%2Fgithub.com%2Feslint%2Feslint.svg?type=large)](https://app.fossa.io/projects/git%2Bhttps%3A%2F%2Fgithub.com%2Feslint%2Feslint?ref=badge_large)
 182
 183 ## <a name="team"></a>Team
 184
 185 These folks keep the project moving and are resources for help.
 186
 187 <!-- NOTE: This section is autogenerated. Do not manually edit.-->
 188 <!--teamstart-->
 189
 190 ### Technical Steering Committee (TSC)
 191
 192 The people who manage releases, review feature requests, and meet regularly to ensure ESLint is properly maintained.
 193
 194 <table><tbody><tr><td align="center" valign="top" width="11%">
 195 <a href="https://github.com/nzakas">
 196 <img src="https://github.com/nzakas.png?s=75" width="75" height="75"><br />
 197 Nicholas C. Zakas
 198 </a>
 199 </td><td align="center" valign="top" width="11%">
 200 <a href="https://github.com/btmills">
 201 <img src="https://github.com/btmills.png?s=75" width="75" height="75"><br />
 202 Brandon Mills
 203 </a>
 204 </td><td align="center" valign="top" width="11%">
 205 <a href="https://github.com/mysticatea">
 206 <img src="https://github.com/mysticatea.png?s=75" width="75" height="75"><br />
 207 Toru Nagashima
 208 </a>
 209 </td><td align="center" valign="top" width="11%">
 210 <a href="https://github.com/kaicataldo">
 211 <img src="https://github.com/kaicataldo.png?s=75" width="75" height="75"><br />
 212 Kai Cataldo
 213 </a>
 214 </td><td align="center" valign="top" width="11%">
 215 <a href="https://github.com/mdjermanovic">
 216 <img src="https://github.com/mdjermanovic.png?s=75" width="75" height="75"><br />
 217 Milos Djermanovic
 218 </a>
 219 </td></tr></tbody></table>
 220
 221
 222 ### Reviewers
 223
 224 The people who review and implement new features.
 225
 226 <table><tbody><tr><td align="center" valign="top" width="11%">
 227 <a href="https://github.com/aladdin-add">
 228 <img src="https://github.com/aladdin-add.png?s=75" width="75" height="75"><br />
 229 薛定谔的猫
 230 </a>
 231 </td></tr></tbody></table>
 232
 233
 234
 235
 236 ### Committers
 237
 238 The people who review and fix bugs and help triage issues.
 239
 240 <table><tbody><tr><td align="center" valign="top" width="11%">
 241 <a href="https://github.com/g-plane">
 242 <img src="https://github.com/g-plane.png?s=75" width="75" height="75"><br />
 243 Pig Fang
 244 </a>
 245 </td><td align="center" valign="top" width="11%">
 246 <a href="https://github.com/anikethsaha">
 247 <img src="https://github.com/anikethsaha.png?s=75" width="75" height="75"><br />
 248 Anix
 249 </a>
 250 </td><td align="center" valign="top" width="11%">
 251 <a href="https://github.com/yeonjuan">
 252 <img src="https://github.com/yeonjuan.png?s=75" width="75" height="75"><br />
 253 YeonJuan
 254 </a>
 255 </td></tr></tbody></table>
 256
 257
 258 <!--teamend-->
 259
 260 ## <a name="sponsors"></a>Sponsors
 261
 262 The following companies, organizations, and individuals support ESLint's ongoing maintenance and development. [Become a Sponsor](https://opencollective.com/eslint) to get your logo on our README and website.
 263
 264 <!-- NOTE: This section is autogenerated. Do not manually edit.-->
 265 <!--sponsorsstart-->
 266 <h3>Platinum Sponsors</h3>
 267 <p><a href="https://automattic.com"><img src="https://images.opencollective.com/photomatt/ff91f0b/logo.png" alt="Automattic" height="undefined"></a></p><h3>Gold Sponsors</h3>
 268 <p><a href="https://www.shopify.com"><img src="https://images.opencollective.com/shopify/e780cd4/logo.png" alt="Shopify" height="96"></a> <a href="https://www.salesforce.com"><img src="https://images.opencollective.com/salesforce/ca8f997/logo.png" alt="Salesforce" height="96"></a> <a href="https://www.airbnb.com/"><img src="https://images.opencollective.com/airbnb/d327d66/logo.png" alt="Airbnb" height="96"></a> <a href="https://aka.ms/microsoftfossfund"><img src="https://avatars1.githubusercontent.com/u/67931232?u=7fddc652a464d7151b97e8f108392af7d54fa3e8&v=4" alt="Microsoft FOSS Fund Sponsorships" height="96"></a></p><h3>Silver Sponsors</h3>
 269 <p><a href="https://liftoff.io/"><img src="https://images.opencollective.com/liftoff/5c4fa84/logo.png" alt="Liftoff" height="64"></a> <a href="https://www.ampproject.org/"><img src="https://images.opencollective.com/amp/c8a3b25/logo.png" alt="AMP Project" height="64"></a></p><h3>Bronze Sponsors</h3>
 270 <p><a href="https://writersperhour.com"><img src="https://images.opencollective.com/writersperhour/5787d4b/logo.png" alt="Writers Per Hour" height="32"></a> <a href="https://www.betacalendars.com/printable-calendar"><img src="https://images.opencollective.com/betacalendars/9334b33/logo.png" alt="2021 calendar" height="32"></a> <a href="https://buy.fineproxy.org/eng/"><img src="https://images.opencollective.com/buy-fineproxy-org/2002c40/logo.png" alt="Buy.Fineproxy.Org" height="32"></a> <a href="https://www.veikkaajat.com"><img src="https://images.opencollective.com/veikkaajat/b92b427/logo.png" alt="Veikkaajat.com" height="32"></a> <a href="https://www.crosswordsolver.org/anagram-solver/"><img src="https://images.opencollective.com/anagram-solver/2666271/logo.png" alt="Anagram Solver" height="32"></a> <a href="null"><img src="https://images.opencollective.com/bugsnag-stability-monitoring/c2cef36/logo.png" alt="Bugsnag Stability Monitoring" height="32"></a> <a href="https://mixpanel.com"><img src="https://images.opencollective.com/mixpanel/cd682f7/logo.png" alt="Mixpanel" height="32"></a> <a href="https://www.vpsserver.com"><img src="https://images.opencollective.com/vpsservercom/logo.png" alt="VPS Server" height="32"></a> <a href="https://icons8.com"><img src="https://images.opencollective.com/icons8/7fa1641/logo.png" alt="Icons8: free icons, photos, illustrations, and music" height="32"></a> <a href="https://discordapp.com"><img src="https://images.opencollective.com/discordapp/7e3d9a9/logo.png" alt="Discord" height="32"></a> <a href="https://themeisle.com"><img src="https://images.opencollective.com/themeisle/d5592fe/logo.png" alt="ThemeIsle" height="32"></a> <a href="https://www.marfeel.com/"><img src="https://images.opencollective.com/marfeel/4b88e30/logo.png" alt="Marfeel" height="32"></a> <a href="https://www.firesticktricks.com"><img src="https://images.opencollective.com/fire-stick-tricks/b8fbe2c/logo.png" alt="Fire Stick Tricks" height="32"></a></p>
 271 <!--sponsorsend-->
 272
 273 ## <a name="technology-sponsors"></a>Technology Sponsors
 274
 275 * Site search ([eslint.org](https://eslint.org)) is sponsored by [Algolia](https://www.algolia.com)
 276 * Hosting for ([eslint.org](https://eslint.org)) is sponsored by [Netlify](https://www.netlify.com)
 277 * Password management is sponsored by [1Password](https://www.1password.com)