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    xo
    DefinitelyTyped icon, indicating that this package has TypeScript declarations provided by the separate @types/xo package

    0.40.0 • Public • Published


    XO


    JavaScript/TypeScript linter (ESLint wrapper) with great defaults

    Coverage Status XO code style

    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 .eslintrc to manage. It just works!

    It uses ESLint underneath, so issues regarding built-in rules should be opened over there.

    XO requires your project to be ESM.

    Highlights

    Install

    $ npm install --global xo
    

    JSX is supported by default, but you'll need eslint-config-xo-react for React specific linting. Vue components are not supported by default. You'll need eslint-config-xo-vue for specific linting in a Vue app.

    Usage

    $ xo --help
    
      Usage
        $ xo [<file|glob> ...]
    
      Options
        --fix             Automagically fix issues
        --reporter        Reporter to use
        --env             Environment preset  [Can be set multiple times]
        --global          Global variable  [Can be set multiple times]
        --ignore          Additional paths to ignore  [Can be set multiple times]
        --space           Use space indent instead of tabs  [Default: 2]
        --no-semicolon    Prevent use of semicolons
        --prettier        Conform to Prettier code style
        --node-version    Range of Node.js version to support
        --plugin          Include third-party plugins  [Can be set multiple times]
        --extend          Extend defaults with a custom config  [Can be set multiple times]
        --open            Open files with issues in your editor
        --quiet           Show only errors and no warnings
        --extension       Additional extension to lint [Can be set multiple times]
        --cwd=<dir>       Working directory for files
        --stdin           Validate/fix code from stdin
        --stdin-filename  Specify a filename for the --stdin option
        --print-config    Print the ESLint configuration for the given file
    
      Examples
        $ xo
        $ xo index.js
        $ xo *.js !foo.js
        $ xo --space
        $ xo --env=node --env=mocha
        $ xo --plugin=react
        $ xo --plugin=html --extension=html
        $ echo 'const x=true' | xo --stdin --fix
        $ xo --print-config=index.js
    
      Tips
        - Add XO to your project with `npm init xo`.
        - Put options in package.json instead of using flags so other tools can read it.
    

    Note that the CLI will use your local install of XO when available, even when run globally.

    Default code style

    Any of these can be overridden if necessary.

    • Tab indentation (or space)
    • Semicolons (or not)
    • Single-quotes
    • No unused variables
    • Space after keyword if (condition) {}
    • Always === instead of ==

    Check out an example and the ESLint rules.

    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 your package.json or create one.

    Before/after

     {
     	"name": "awesome-package",
     	"scripts": {
    -		"test": "ava",
    +		"test": "xo && ava"
     	},
     	"devDependencies": {
    -		"ava": "^2.0.0"
    +		"ava": "^2.0.0",
    +		"xo": "^0.25.0"
     	}
     }

    Then just run $ npm test and XO will be run before your tests.

    Config

    You can configure XO options with one of the following files:

    1. As JSON in the xo property in package.json:
    {
    	"name": "awesome-package",
    	"xo": {
    		"space": true
    	}
    }
    1. As JSON in .xo-config or .xo-config.json:
    {
    	"space": true
    }
    1. As a JavaScript module in .xo-config.js or xo.config.js:
    module.exports = {
    	space: true
    };

    Globals and rules can be configured inline in files.

    envs

    Type: string[]
    Default: ['es2021', 'node']

    Which environments your code is designed to run in. Each environment brings with it a certain set of predefined global variables.

    globals

    Type: string[]

    Additional global variables your code accesses during execution.

    ignores

    Type: string[]

    Some paths are ignored by default, including paths in .gitignore and .eslintignore. Additional ignores can be added here.

    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".

    rules

    Type: object

    Override any of the default rules. See the ESLint docs for more info on each rule.

    Please take a moment to consider if you really need to use this option.

    semicolon

    Type: boolean
    Default: true (Semicolons required)

    Set it to false to enforce no-semicolon style.

    prettier

    Type: boolean
    Default: false

    Format code with Prettier.

    The Prettier options will be read from the Prettier config and if not set will be determined as follow:

    If contradicting options are set for both Prettier and XO an error will be thrown.

    nodeVersion

    Type: string | boolean
    Default: Value of the engines.node key in the project package.json

    Enable rules specific to the Node.js versions within the configured range.

    If set to false, no rules specific to a Node.js version will be enabled.

    plugins

    Type: string[]

    Include third-party plugins.

    extends

    Type: string | string[]

    Use one or more shareable configs or plugin configs to override any of the default rules (like rules above).

    extensions

    Type: string[]

    Allow more extensions to be linted besides .js, .jsx, .mjs, and .cjs. Make sure they're supported by ESLint or an ESLint plugin.

    settings

    Type: object

    Shared ESLint settings exposed to rules.

    parser

    Type: string

    ESLint parser. For example, @babel/eslint-parser if you're using language features that ESLint doesn't yet support.

    processor

    Type: string

    ESLint processor.

    webpack

    Type: boolean | object Default: false

    Use eslint-import-resolver-webpack to resolve import search paths. This is enabled automatically if a webpack.config.js file is found.

    Set this to a boolean to explicitly enable or disable the resolver.

    Setting this to an object enables the resolver and passes the object as configuration. See the resolver readme along with the webpack documentation for more information.

    TypeScript

    XO will automatically lint TypeScript files (.ts, .d.ts and .tsx) with the rules defined in eslint-config-xo-typescript#use-with-xo.

    XO will handle the @typescript-eslint/parser project option automatically even if you don't have a tsconfig.json in your project.

    GitHub Actions

    XO uses a different formatter when running in a GitHub Actions workflow to be able to get inline annotations. XO also disables warnings here.

    Note: For this to work, the setup-node action must be run before XO.

    Config Overrides

    XO makes it easy to override configs for specific files. The overrides property must be an array of override objects. Each override object must contain a files property which is a glob string, or an array of glob strings, relative to the config file. The remaining properties are identical to those described above, and will override the settings of the base config. If multiple override configs match the same file, each matching override is applied in the order it appears in the array. This means the last override in the array takes precedence over earlier ones. Consider the following example:

    {
    	"xo": {
    		"semicolon": false,
    		"space": 2,
    		"overrides": [
    			{
    				"files": "test/*.js",
    				"space": 3
    			},
    			{
    				 "files": "test/foo.js",
    				 "semicolon": true
    			}
    		]
    	}
    }
    • The base configuration is simply space: 2, semicolon: false. These settings are used for every file unless otherwise noted below.

    • For every file in test/*.js, the base config is used, but space is overridden with 3. The resulting config is:

    {
    	"semicolon": false,
    	"space": 3
    }
    • For test/foo.js, the base config is first applied, followed the first overrides config (its glob pattern also matches test/foo.js), finally the second override config is applied. The resulting config is:
    {
    	"semicolon": true,
    	"space": 3
    }

    Tips

    Using a parent's config

    If you have a directory structure with nested package.json files and you want one of the child manifests to be skipped, you can do so by ommiting the xo property in the child's package.json. For example, when you have separate app and dev package.json files with electron-builder.

    Monorepo

    Put a package.json with your config at the root and omit the xo property in the package.json of your bundled packages.

    Transpilation

    If some files in your project are transpiled in order to support an older Node.js version, you can use the config overrides option to set a specific nodeVersion to target your sources files.

    For example, if your project targets Node.js 8 but you want to use the latest JavaScript syntax as supported in Node.js 12:

    1. Set the engines.node property of your package.json to >=8
    2. Configure Babel to transpile your source files (in src directory in this example)
    3. Make sure to include the transpiled files in your published package with the files and main properties of your package.json
    4. Configure the XO overrides option to set nodeVersion to >=12 for your source files directory
    {
    	"engines": {
    		"node": ">=12"
    	},
    	"scripts": {
    		"build": "babel src --out-dir dist"
    	},
    	"main": "dist/index.js",
    	"files": ["dist/**/*.js"],
    	"xo": {
    		"overrides": [
    			{
    				"files": "{src}/**/*.js",
    				"nodeVersion": ">=16"
    			}
    		]
    	}
    }

    This way your package.json will contain the actual minimum Node.js version supported by your published code, but XO will lint your source code as if it targets Node.js 16.

    Including files ignored by default

    To include files that XO ignores by default, add them as negative globs in the ignores option:

    {
    	"xo": {
    		"ignores": [
    			"!vendor/**"
    		]
    	}
    }

    FAQ

    What does XO mean?

    It means hugs and kisses.

    Why not Standard?

    The Standard style 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.

    Editor plugins

    Build-system plugins

    Configs

    Support

    Related

    Badge

    Show the world you're using XO → XO code style

    [![XO code style](https://img.shields.io/badge/code_style-XO-5ed9c7.svg)](https://github.com/xojs/xo)

    You can also find some nice dynamic XO badges on badgen.net.

    Team

    Former

    Install

    npm i xo

    DownloadsWeekly Downloads

    38,329

    Version

    0.40.0

    License

    MIT

    Unpacked Size

    65.6 kB

    Total Files

    11

    Last publish

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