JavaScript/TypeScript linter (ESLint wrapper) with great defaults
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.
unicorn, import, ava, n and more.engines field in your package.json.$ npm init xo.$ xo --fix.$ xo --open.npm install xo --save-dev
You must install XO locally. You can run it directly with $ npx 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.
$ 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.
Any of these can be overridden if necessary.
if (condition) {}=== instead of ==Check out an example and the ESLint rules.
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.
{
"name": "awesome-package",
"scripts": {
- "test": "ava",
+ "test": "xo && ava"
},
"devDependencies": {
- "ava": "^3.0.0"
+ "ava": "^3.0.0",
+ "xo": "^0.41.0"
}
}
Then just run $ npm test and XO will be run before your tests.
You can configure XO options with one of the following files:
xo property in package.json:{
"name": "awesome-package",
"xo": {
"space": true
}
}
.xo-config or .xo-config.json:{
"space": true
}
.xo-config.js or xo.config.js:module.exports = {
space: true
};
"type": "module", as a JavaScript module in .xo-config.cjs or xo.config.cjs:module.exports = {
space: true
};
Globals and rules can be configured inline in files.
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.
Type: string[]
Additional global variables your code accesses during execution.
Type: string[]
Some paths are ignored by default, including paths in .gitignore and .eslintignore. Additional ignores can be added here.
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".
Type: object
Override any of the default rules. See the ESLint docs for more info on each rule.
Disable a rule in your XO config to turn it off globally in your project.
Example using package.json:
{
"xo": {
"rules": {
"unicorn/no-array-for-each": "off"
}
}
}
You could also use .xo-config.json or one of the other config file formats supported by XO.
Please take a moment to consider if you really need to use this option.
Type: boolean
Default: true (Semicolons required)
Set it to false to enforce no-semicolon style.
Type: boolean
Default: false
Format code with Prettier.
Prettier options will be based on your Prettier config. XO will then merge your options with its own defaults:
alltruefalseTo stick with Prettier's defaults, add this to your Prettier config:
module.exports = {
trailingComma: 'es5',
singleQuote: false,
bracketSpacing: true,
};
If contradicting options are set for both Prettier and XO, an error will be thrown.
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.
Type: string[]
Include third-party plugins.
Type: string | string[]
Use one or more shareable configs or plugin configs to override any of the default rules (like rules above).
Type: string[]
Allow more extensions to be linted besides .js, .jsx, .mjs, and .cjs as well as their TypeScript equivalents .ts, .tsx, .mts and .cts. Make sure they're supported by ESLint or an ESLint plugin.
Type: object
Shared ESLint settings exposed to rules.
Type: string
ESLint parser. For example, @babel/eslint-parser if you're using language features that ESLint doesn't yet support.
Type: string
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.
XO will automatically lint TypeScript files (.ts, .mts, .cts, .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.
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.
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
}
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
}
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.
Put a package.json with your config at the root and omit the xo property in the package.json of your bundled packages.
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:
engines.node property of your package.json to >=8source directory in this example)files and main properties of your package.jsonoverrides option to set nodeVersion to >=12 for your source files directory{
"engines": {
"node": ">=12"
},
"scripts": {
"build": "babel source --out-dir distribution"
},
"main": "distribution/index.js",
"files": [
"distribution/**/*.js"
],
"xo": {
"overrides": [
{
"files": "source/**/*.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.
To include files that XO ignores by default, add them as negative globs in the ignores option:
{
"xo": {
"ignores": [
"!vendor/**"
]
}
}
It means hugs and kisses.
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.
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.
xo as a list of style errors, ordered by countShow the world you're using XO →
[](https://github.com/xojs/xo)
You can also find some nice dynamic XO badges on badgen.net.
FAQs
JavaScript/TypeScript linter (ESLint wrapper) with great defaults
The npm package xo receives a total of 77,544 weekly downloads. As such, xo popularity was classified as popular.
We found that xo demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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