xo
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JavaScript/TypeScript linter (ESLint wrapper) with great defaults
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Markdown
<h1 align="center">
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<img width="400" src="media/logo.svg" alt="XO">
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</h1>
> JavaScript/TypeScript linter (ESLint wrapper) with great defaults
[](https://codecov.io/gh/xojs/xo/branch/main)
[](https://github.com/xojs/xo)
Opinionated but configurable ESLint wrapper with lots of goodies included. Enforces strict and readable code. Never discuss code style on a pull request again! No decision-making. No `eslint.config.js` to manage. It just works!
It uses [ESLint](https://eslint.org) underneath, so issues regarding built-in rules should be opened over [there](https://github.com/eslint/eslint/issues).
**XO requires your project to be [ESM](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c).**
## Highlights
- Beautiful output.
- Zero-config, but [configurable when needed](#config).
- Enforces readable code, because you read more code than you write.
- No need to specify file paths to lint as it lints all JS/TS files except for [commonly ignored paths](#ignores).
- [Flat config customization.](#config)
- [TypeScript supported by default.](#typescript)
- Includes many useful ESLint plugins, like [`unicorn`](https://github.com/sindresorhus/eslint-plugin-unicorn), [`import`](https://github.com/benmosher/eslint-plugin-import), [`ava`](https://github.com/avajs/eslint-plugin-ava), [`n`](https://github.com/eslint-community/eslint-plugin-n) and more.
- Caches results between runs for much better performance.
- Super simple to add XO to a project with [`$ npm init xo`](https://github.com/xojs/create-xo).
- Fix many issues automagically with `$ xo --fix`.
- Open all files with errors at the correct line in your editor with `$ xo --open`.
- Specify [indent](#space) and [semicolon](#semicolon) preferences easily without messing with the rule config.
- Optionally use the [Prettier](https://github.com/prettier/prettier) code style or turn off all Prettier rules with the `compat` option.
- Optionally use `eslint-config-xo-react` for easy jsx and react linting with zero config.
- Optionally use with ESLint [directly](#usage-as-an-eslint-configuration)
- Great [editor plugins](#editor-plugins).
## Install
```sh
npm install xo --save-dev
```
*You must install XO locally. You can run it directly with `$ npx xo`.*
*You'll need [eslint-config-xo-vue](https://github.com/ChocPanda/eslint-config-xo-vue#use-with-xo) for specific linting in a Vue app.*
## Usage
```
$ xo --help
Usage
$ xo [<file|glob> ...]
Options
--fix Automagically fix issues
--reporter Reporter to use
--space Use space indent instead of tabs [Default: 2]
--config Path to a XO configuration file
--semicolon Use semicolons [Default: true]
--react Include React specific parsing and xo-react linting rules [Default: false]
--prettier Format with prettier or turn off prettier conflicted rules when set to 'compat' [Default: false]
--print-config Print the effective ESLint config for the given file
--version Print XO version
--open Open files with issues in your editor
--quiet Show only errors and no warnings
--stdin Validate/fix code from stdin
--stdin-filename Specify a filename for the --stdin option
--ignore Ignore pattern globs, can be set multiple times
--cwd=<dir> Working directory for files [Default: process.cwd()]
Examples
$ xo
$ xo index.js
$ xo *.js !foo.js
$ xo --space
$ xo --print-config=index.js
$ echo 'const x=true' | xo --stdin --fix
Tips
- Add XO to your project with `npm init xo`.
- Put options in xo.config.js instead of using flags so other tools can read it.
```
## Default code style
*Any of these can be [overridden](#rules) if necessary.*
- Tab indentation *[(or space)](#space)*
- Semicolons *[(or not)](#semicolon)*
- Single-quotes
- [Trailing comma](https://medium.com/@nikgraf/why-you-should-enforce-dangling-commas-for-multiline-statements-d034c98e36f8) for multiline statements
- No unused variables
- Space after keyword `if (condition) {}`
- Always `===` instead of `==`
Check out an [example](index.ts) and the [ESLint rules](https://github.com/xojs/eslint-config-xo/blob/main/index.js).
## Workflow
The recommended workflow is to add XO locally to your project and run it with the tests.
Simply run `$ npm init xo` (with any options) to add XO to create an `xo.config.js`.
## Config
You can configure XO options by creating an `xo.config.js` or an `xo.config.ts` file in the root directory of your project. XO supports all js/ts file extensions (js,cjs,mjs,ts,cts,mts) automatically. A XO config is an extension of ESLint's Flat Config. Like ESLint, an XO config exports an array of XO config objects. XO config objects extend [ESLint Configuration Objects](https://eslint.org/docs/latest/use/configure/configuration-files#configuration-objects). This means all the available configuration params for ESLint also work for `XO`. However, `XO` enhances and adds extra params to the configuration objects to make them easier to work with.
### Config types
XO exports the types `FlatXoConfig`, `XoConfigItem`, and other types for you to get TypeScript validation on your config files.
examples:
`xo.config.js`
```js
/** @type {import('xo').FlatXoConfig} */
const xoConfig = [...]
```
`xo.config.ts`
```js
import {type FlatXoConfig} from 'xo';
const xoConfig: FlatXoConfig = [...]
```
### files
Type: `string | string[] | undefined`\
Default: `**/*.{js,cjs,mjs,jsx,ts,cts,mts,tsx}`
A glob or array of glob strings which the config object will apply. By default `XO` will apply the configuration to [all files](lib/constants.ts).
### ignores
Type: `string[]`
Some [paths](lib/constants.ts) are ignored by default, including paths in `.gitignore`. Additional ignores can be added here. For global ignores, keep `ignores` as the only key in the config item.
### space
Type: `boolean | number`\
Default: `false` *(tab indentation)*
Set it to `true` to get 2-space indentation or specify the number of spaces.
This option exists for pragmatic reasons, but I would strongly recommend you read [“Why tabs are superior”](http://lea.verou.me/2012/01/why-tabs-are-clearly-superior/).
### semicolon
Type: `boolean`\
Default: `true` *(Semicolons required)*
Set it to `false` to enforce no-semicolon style.
### prettier
Type: `boolean | 'compat'`\
Default: `false`
Format code with [Prettier](https://github.com/prettier/prettier).
[Prettier options](https://prettier.io/docs/en/options.html) will be based on your [Prettier config](https://prettier.io/docs/en/configuration.html). XO will then **merge** your options with its own defaults:
- [semi](https://prettier.io/docs/en/options.html#semicolons): based on [semicolon](#semicolon) option
- [useTabs](https://prettier.io/docs/en/options.html#tabs): based on [space](#space) option
- [tabWidth](https://prettier.io/docs/en/options.html#tab-width): based on [space](#space) option
- [singleQuote](https://prettier.io/docs/en/options.html#quotes): `true`
- [bracketSpacing](https://prettier.io/docs/en/options.html#bracket-spacing): `false`
To stick with Prettier's defaults, add this to your Prettier config:
```js
export default {
singleQuote: false,
bracketSpacing: true,
};
```
If contradicting options are set for both Prettier and XO, an error will be thrown.
#### Compat
If the Prettier option is set to `compat`, instead of formatting your code automatically, XO will turn off all rules that conflict with Prettier code style and allow you to pass your formatting to the Prettier tool directly.
### react
Type: `boolean`\
Default: `false`
Adds `eslint-plugin-react`, `eslint-plugin-react-hooks`, and `eslint-config-xo-react` to get all the React best practices applied automatically.
## TypeScript
XO will automatically lint TypeScript files (`.ts`, `.mts`, `.cts`, and `.tsx`) with the rules defined in [eslint-config-xo-typescript#use-with-xo](https://github.com/xojs/eslint-config-xo-typescript#use-with-xo).
XO will handle the [@typescript-eslint/parser `project` option](https://typescript-eslint.io/packages/parser/#project) automatically even if you don't have a `tsconfig.json` in your project.
## Usage as an ESLint Configuration
With the introduction of the ESLint flat config, many of the original goals of `xo` were brought into the ESLint core, and shareable configs with plugins became possible. Although we highly recommend the use of the `xo` cli, we understand that some teams need to rely on ESLint directly.
For these purposes, you can still get most of the features of `xo` by using our ESLint configuration helpers.
### `xoToEslintConfig`
The `xoToEslintConfig` function is designed for use in an `eslint.config.js` file. It is NOT for use in an `xo.config.js` file. This function takes a `FlatXoConfig` and outputs an ESLint config object. This function will neither be able to automatically handle TS integration for you nor automatic Prettier integration. You are responsible for configuring your other tools appropriately. The `xo` cli, will however, handle all of these details for you.
`eslint.config.js`
```js
import xo from 'xo';
export default xo.xoToEslintConfig([{space: true, prettier: 'compat'}]);
```
## Tips
### Monorepo
Put a `xo.config.js` with your config at the root and do not add a config to any of your bundled packages.
### Including files ignored by default
To include files that XO [ignores by default](lib/constants.ts), add them as negative globs in the [`ignores` option](#ignores):
```js
const xoConfig = [{ignores: ['!vendor/**']}];
export default xoConfig;
```
## FAQ
#### What does XO mean?
It means [hugs and kisses](https://en.wiktionary.org/wiki/xoxo).
#### Why not Standard?
The [Standard style](https://standardjs.com) is a really cool idea. I too wish we could have one style to rule them all! But the reality is that the JS community is just too diverse and opinionated to create *one* code style. They also made the mistake of pushing their own style instead of the most popular one. In contrast, XO is more pragmatic and has no aspiration of being *the* style. My goal with XO is to make it simple to enforce consistent code style with close to no config. XO comes with my code style preference by default, as I mainly made it for myself, but everything is configurable.
#### Why not ESLint?
XO is based on ESLint. This project started out as just a shareable ESLint config, but it quickly grew out of that. I wanted something even simpler. Just typing `xo` and be done. No decision-making. No config. I also have some exciting future plans for it. However, you can still get most of the XO benefits while using ESLint directly with the [ESLint shareable config](https://github.com/xojs/eslint-config-xo).
## Editor plugins
- [Sublime Text](https://github.com/xojs/SublimeLinter-contrib-xo)
- [Atom](https://github.com/xojs/atom-linter-xo)
- [Vim](https://github.com/xojs/vim-xo)
- [TextMate 2](https://github.com/claylo/XO.tmbundle)
- [VSCode](https://github.com/SamVerschueren/vscode-linter-xo)
- [Emacs](https://github.com/j-em/xo-emacs)
- [WebStorm](https://github.com/jamestalmage/xo-with-webstorm)
## Build-system plugins
- [Gulp](https://github.com/xojs/gulp-xo)
- [Grunt](https://github.com/xojs/grunt-xo)
- [webpack loader](https://github.com/Semigradsky/xo-loader)
- [webpack plugin](https://github.com/nstanard/xo-webpack-plugin)
- [Metalsmith](https://github.com/blainsmith/metalsmith-xo)
- [Fly](https://github.com/lukeed/fly-xo)
## Configs
- [eslint-config-xo](https://github.com/xojs/eslint-config-xo) - ESLint shareable config for XO with tab indent
- [eslint-config-xo-space](https://github.com/xojs/eslint-config-xo-space) - ESLint shareable config for XO with 2-space indent
- [eslint-config-xo-react](https://github.com/xojs/eslint-config-xo-react) - ESLint shareable config for React to be used with the above
- [eslint-config-xo-vue](https://github.com/ChocPanda/eslint-config-xo-vue) - ESLint shareable config for Vue to be used with the above
- [stylelint-config-xo](https://github.com/xojs/stylelint-config-xo) - Stylelint shareable config for XO with tab indent
- [stylelint-config-xo-space](https://github.com/xojs/stylelint-config-xo-space) - Stylelint shareable config for XO with 2-space indent
- [eslint-config-xo-typescript](https://github.com/xojs/eslint-config-xo-typescript) - ESLint shareable config for TypeScript
## Support
- [Twitter](https://twitter.com/sindresorhus)
## Related
- [eslint-plugin-unicorn](https://github.com/sindresorhus/eslint-plugin-unicorn) - Various awesome ESLint rules *(Bundled in XO)*
- [xo-summary](https://github.com/LitoMore/xo-summary) - Display output from `xo` as a list of style errors, ordered by count
## Badge
Show the world you're using XO → [](https://github.com/xojs/xo)
```md
[](https://github.com/xojs/xo)
```
Or [customize the badge](https://github.com/xojs/xo/issues/689#issuecomment-1253127616).
You can also find some nice dynamic XO badges on [badgen.net](https://badgen.net/#xo).
## Team
- [Sindre Sorhus](https://github.com/sindresorhus)
###### Former
- [James Talmage](https://github.com/jamestalmage)
- [Michael Mayer](https://github.com/schnittstabil)
- [Mario Nebl](https://github.com/marionebl)
- [Pierre Vanduynslager](https://github.com/pvdlg)