🚫💩 lint-staged

Run linters against staged git files and don't let :poop: slip into your code base!

$ git commit

✔ Preparing lint-staged...
❯ Running tasks for staged files...
  ❯ packages/frontend/.lintstagedrc.json — 1 file
    ↓ *.js — no files [SKIPPED]
    ❯ *.{json,md} — 1 file
      ⠹ prettier --write
  ↓ packages/backend/.lintstagedrc.json — 2 files
    ❯ *.js — 2 files
      ⠼ eslint --fix
    ↓ *.{json,md} — no files [SKIPPED]
◼ Applying modifications from tasks...
◼ Cleaning up temporary files...

Why

Linting makes more sense when run before committing your code. By doing so you can ensure no errors go into the repository and enforce code style. But running a lint process on a whole project is slow, and linting results can be irrelevant. Ultimately you only want to lint files that will be committed.

This project contains a script that will run arbitrary shell tasks with a list of staged files as an argument, filtered by a specified glob pattern.

Related blog posts and talks

• Introductory Medium post - Andrey Okonetchnikov, 2016
• Running Jest Tests Before Each Git Commit - Ben McCormick, 2017
• AgentConf presentation - Andrey Okonetchnikov, 2018
• SurviveJS interview - Juho Vepsäläinen and Andrey Okonetchnikov, 2018
• Prettier your CSharp with dotnet-format and lint-staged

If you've written one, please submit a PR with the link to it!

Installation and setup

The fastest way to start using lint-staged is to run the following command in your terminal:

npx mrm@2 lint-staged

This command will install and configure husky and lint-staged depending on the code quality tools from your project's package.json dependencies, so please make sure you install (npm install --save-dev) and configure all code quality tools like Prettier and ESLint prior to that.

Don't forget to commit changes to package.json and .husky to share this setup with your team!

Now change a few files, git add or git add --patch some of them to your commit, and try to git commit them.

See examples and configuration for more information.

Changelog

See Releases.

Migration

v12

• Since v12.0.0 lint-staged is a pure ESM module, so make sure your Node.js version is at least 12.20.0, 14.13.1, or 16.0.0. Read more about ESM modules from the official Node.js Documentation site here.

v10

• From v10.0.0 onwards any new modifications to originally staged files will be automatically added to the commit. If your task previously contained a git add step, please remove this. The automatic behaviour ensures there are less race-conditions, since trying to run multiple git operations at the same time usually results in an error.
• From v10.0.0 onwards, lint-staged uses git stashes to improve speed and provide backups while running. Since git stashes require at least an initial commit, you shouldn't run lint-staged in an empty repo.
• From v10.0.0 onwards, lint-staged requires Node.js version 10.13.0 or later.
• From v10.0.0 onwards, lint-staged will abort the commit if linter tasks undo all staged changes. To allow creating an empty commit, please use the --allow-empty option.

Command line flags

❯ npx lint-staged --help
Usage: lint-staged [options]

Options:
  -V, --version                      output the version number
  --allow-empty                      allow empty commits when tasks revert all staged changes (default: false)
  -p, --concurrent <number|boolean>  the number of tasks to run concurrently, or false for serial (default: true)
  -c, --config [path]                path to configuration file, or - to read from stdin
  --cwd [path]                       run all tasks in specific directory, instead of the current
  -d, --debug                        print additional debug information (default: false)
  --no-stash                         disable the backup stash, and do not revert in case of errors
  -q, --quiet                        disable lint-staged’s own console output (default: false)
  -r, --relative                     pass relative filepaths to tasks (default: false)
  -x, --shell [path]                 skip parsing of tasks for better shell support (default: false)
  -v, --verbose                      show task output even when tasks succeed; by default only failed output is shown
                                     (default: false)
  -h, --help                         display help for command

• --allow-empty: By default, when linter tasks undo all staged changes, lint-staged will exit with an error and abort the commit. Use this flag to allow creating empty git commits.
• --concurrent [number|boolean]: Controls the concurrency of tasks being run by lint-staged. NOTE: This does NOT affect the concurrency of subtasks (they will always be run sequentially). Possible values are:
  • false: Run all tasks serially
  • true (default) : Infinite concurrency. Runs as many tasks in parallel as possible.
  • {number}: Run the specified number of tasks in parallel, where 1 is equivalent to false.
• --config [path]: Manually specify a path to a config file or npm package name. Note: when used, lint-staged won't perform the config file search and will print an error if the specified file cannot be found. If '-' is provided as the filename then the config will be read from stdin, allowing piping in the config like cat my-config.json | npx lint-staged --config -.
• --cwd [path]: By default tasks run in the current working directory. Use the --cwd some/directory to override this. The path can be absolute or relative to the current working directory.
• --debug: Run in debug mode. When set, it does the following:
  • uses debug internally to log additional information about staged files, commands being executed, location of binaries, etc. Debug logs, which are automatically enabled by passing the flag, can also be enabled by setting the environment variable $DEBUG to lint-staged*.
  • uses verbose renderer for listr; this causes serial, uncoloured output to the terminal, instead of the default (beautified, dynamic) output.
• --no-stash: By default a backup stash will be created before running the tasks, and all task modifications will be reverted in case of an error. This option will disable creating the stash, and instead leave all modifications in the index when aborting the commit.
• --quiet: Supress all CLI output, except from tasks.
• --relative: Pass filepaths relative to process.cwd() (where lint-staged runs) to tasks. Default is false.
• --shell: By default linter commands will be parsed for speed and security. This has the side-effect that regular shell scripts might not work as expected. You can skip parsing of commands with this option. To use a specific shell, use a path like --shell "/bin/bash".
• --verbose: Show task output even when tasks succeed. By default only failed output is shown.

Configuration

Starting with v3.1 you can now use different ways of configuring lint-staged:

• lint-staged object in your package.json
• .lintstagedrc file in JSON or YML format, or you can be explicit with the file extension:
  • .lintstagedrc.json
  • .lintstagedrc.yaml
  • .lintstagedrc.yml
• .lintstagedrc.mjs or lint-staged.config.mjs file in ESM format
  • the default export value should be a configuration: export default { ... }
• .lintstagedrc.cjs or lint-staged.config.cjs file in CommonJS format
  • the exports value should be a configuration: module.exports = { ... }
• lint-staged.config.js or .lintstagedrc.js in either ESM or CommonJS format, depending on whether your project's package.json contains the "type": "module" option or not.
• Pass a configuration file using the --config or -c flag

Configuration should be an object where each value is a command to run and its key is a glob pattern to use for this command. This package uses micromatch for glob patterns. JavaScript files can also export advanced configuration as a function. See Using JS configuration files for more info.

You can also place multiple configuration files in different directories inside a project. For a given staged file, the closest configuration file will always be used. See "How to use lint-staged in a multi-package monorepo?" for more info and an example.

package.json example:

{
  "lint-staged": {
    "*": "your-cmd"
  }
}

.lintstagedrc example

{
  "*": "your-cmd"
}

This config will execute your-cmd with the list of currently staged files passed as arguments.

So, considering you did git add file1.ext file2.ext, lint-staged will run the following command:

your-cmd file1.ext file2.ext

Filtering files

Linter commands work on a subset of all staged files, defined by a glob pattern. lint-staged uses micromatch for matching files with the following rules:

• If the glob pattern contains no slashes (/), micromatch's matchBase option will enabled, so globs match a file's basename regardless of directory:
  • "*.js" will match all JS files, like /test.js and /foo/bar/test.js
  • "!(*test).js". will match all JS files, except those ending in test.js, so foo.js but not foo.test.js
• If the glob pattern does contain a slash (/), it will match for paths as well:
  • "./*.js" will match all JS files in the git repo root, so /test.js but not /foo/bar/test.js
  • "foo/**/\*.js" will match all JS files inside the/foodirectory, so/foo/bar/test.jsbut not/test.js

When matching, lint-staged will do the following

• Resolve the git root automatically, no configuration needed.
• Pick the staged files which are present inside the project directory.
• Filter them using the specified glob patterns.
• Pass absolute paths to the linters as arguments.

NOTE: lint-staged will pass absolute paths to the linters to avoid any confusion in case they're executed in a different working directory (i.e. when your .git directory isn't the same as your package.json directory).

Also see How to use lint-staged in a multi-package monorepo?

Ignoring files

The concept of lint-staged is to run configured linter tasks (or other tasks) on files that are staged in git. lint-staged will always pass a list of all staged files to the task, and ignoring any files should be configured in the task itself.

Consider a project that uses prettier to keep code format consistent across all files. The project also stores minified 3rd-party vendor libraries in the vendor/ directory. To keep prettier from throwing errors on these files, the vendor directory should be added to prettier's ignore configuration, the .prettierignore file. Running npx prettier . will ignore the entire vendor directory, throwing no errors. When lint-staged is added to the project and configured to run prettier, all modified and staged files in the vendor directory will be ignored by prettier, even though it receives them as input.

In advanced scenarios, where it is impossible to configure the linter task itself to ignore files, but some staged files should still be ignored by lint-staged, it is possible to filter filepaths before passing them to tasks by using the function syntax. See Example: Ignore files from match.

What commands are supported?

Supported are any executables installed locally or globally via npm as well as any executable from your $PATH.

Using globally installed scripts is discouraged, since lint-staged may not work for someone who doesn't have it installed.

lint-staged uses execa to locate locally installed scripts. So in your .lintstagedrc you can write:

{
  "*.js": "eslint --fix"
}

Pass arguments to your commands separated by space as you would do in the shell. See examples below.

Running multiple commands in a sequence

You can run multiple commands in a sequence on every glob. To do so, pass an array of commands instead of a single one. This is useful for running autoformatting tools like eslint --fix or stylefmt but can be used for any arbitrary sequences.

For example:

{
  "*.js": ["eslint", "prettier --write"]
}

going to execute eslint and if it exits with 0 code, it will execute prettier --write on all staged *.js files.

Using JS configuration files

Writing the configuration file in JavaScript is the most powerful way to configure lint-staged (lint-staged.config.js, similar, or passed via --config). From the configuration file, you can export either a single function or an object.

If the exports value is a function, it will receive an array of all staged filenames. You can then build your own matchers for the files and return a command string or an array of command strings. These strings are considered complete and should include the filename arguments, if wanted.

If the exports value is an object, its keys should be glob matches (like in the normal non-js config format). The values can either be like in the normal config or individual functions like described above. Instead of receiving all matched files, the functions in the exported object will only receive the staged files matching the corresponding glob key.

Function signature

The function can also be async:

(filenames: string[]) => string | string[] | Promise<string | string[]>

Example: Export a function to build your own matchers

// lint-staged.config.js
import micromatch from 'micromatch'

export default (allStagedFiles) => {
  const shFiles = micromatch(allStagedFiles, ['**/src/**/*.sh'])
  if (shFiles.length) {
    return `printf '%s\n' "Script files aren't allowed in src directory" >&2`
  }
  const codeFiles = micromatch(allStagedFiles, ['**/*.js', '**/*.ts'])
  const docFiles = micromatch(allStagedFiles, ['**/*.md'])
  return [`eslint ${codeFiles.join(' ')}`, `mdl ${docFiles.join(' ')}`]
}

Example: Wrap filenames in single quotes and run once per file

// .lintstagedrc.js
export default {
  '**/*.js?(x)': (filenames) => filenames.map((filename) => `prettier --write '${filename}'`),
}

Example: Run tsc on changes to TypeScript files, but do not pass any filename arguments

// lint-staged.config.js
export default {
  '**/*.ts?(x)': () => 'tsc -p tsconfig.json --noEmit',
}

Example: Run ESLint on entire repo if more than 10 staged files

// .lintstagedrc.js
export default {
  '**/*.js?(x)': (filenames) =>
    filenames.length > 10 ? 'eslint .' : `eslint ${filenames.join(' ')}`,
}

Example: Use your own globs

// lint-staged.config.js
import micromatch from 'micromatch'

export default {
  '*': (allFiles) => {
    const codeFiles = micromatch(allFiles, ['**/*.js', '**/*.ts'])
    const docFiles = micromatch(allFiles, ['**/*.md'])
    return [`eslint ${codeFiles.join(' ')}`, `mdl ${docFiles.join(' ')}`]
  },
}

Example: Ignore files from match

// lint-staged.config.js
import micromatch from 'micromatch'

export default {
  '*.js': (files) => {
    // from `files` filter those _NOT_ matching `*test.js`
    const match = micromatch.not(files, '*test.js')
    return `eslint ${match.join(' ')}`
  },
}

Example: Use relative paths for commands

import path from 'path'

export default {
  '*.ts': (absolutePaths) => {
    const cwd = process.cwd()
    const relativePaths = absolutePaths.map((file) => path.relative(cwd, file))
    return `ng lint myProjectName --files ${relativePaths.join(' ')}`
  },
}

Reformatting the code

Tools like Prettier, ESLint/TSLint, or stylelint can reformat your code according to an appropriate config by running prettier --write/eslint --fix/tslint --fix/stylelint --fix. Lint-staged will automatically add any modifications to the commit as long as there are no errors.

{
  "*.js": "prettier --write"
}

Prior to version 10, tasks had to manually include git add as the final step. This behavior has been integrated into lint-staged itself in order to prevent race conditions with multiple tasks editing the same files. If lint-staged detects git add in task configurations, it will show a warning in the console. Please remove git add from your configuration after upgrading.

Examples

All examples assume you've already set up lint-staged in the package.json file and husky in its own config file.

{
  "name": "My project",
  "version": "0.1.0",
  "scripts": {
    "my-custom-script": "linter --arg1 --arg2"
  },
  "lint-staged": {}
}

In .husky/pre-commit

#!/usr/bin/env sh
. "$(dirname "$0")/_/husky.sh"

npx lint-staged

Note: we don't pass a path as an argument for the runners. This is important since lint-staged will do this for you.

ESLint with default parameters for *.js and *.jsx running as a pre-commit hook

{
  "*.{js,jsx}": "eslint"
}

Automatically fix code style with --fix and add to commit

{
  "*.js": "eslint --fix"
}

Reuse npm script

{
  "*.js": "npm run my-custom-script --"
}

{
  "*.js": "linter --arg1 --arg2"
}

Use environment variables with linting commands

{
  "*.js": ["cross-env NODE_ENV=test jest --bail --findRelatedTests"]
}

Automatically fix code style with prettier for any format Prettier supports

{
  "*": "prettier --ignore-unknown --write"
}

Automatically fix code style with prettier for JavaScript, TypeScript, Markdown, HTML, or CSS

{
  "*.{js,jsx,ts,tsx,md,html,css}": "prettier --write"
}

Stylelint for CSS with defaults and for SCSS with SCSS syntax

{
  "*.css": "stylelint",
  "*.scss": "stylelint --syntax=scss"
}

Run PostCSS sorting and Stylelint to check

{
  "*.scss": ["postcss --config path/to/your/config --replace", "stylelint"]
}

Minify the images

{
  "*.{png,jpeg,jpg,gif,svg}": "imagemin-lint-staged"
}

Typecheck your staged files with flow

{
  "*.{js,jsx}": "flow focus-check"
}

Frequently Asked Questions

Can I use lint-staged via node?

import lintStaged from 'lint-staged'

try {
  const success = await lintStaged()
  console.log(success ? 'Linting was successful!' : 'Linting failed!')
} catch (e) {
  // Failed to load configuration
  console.error(e)
}

const success = await lintStaged({
  allowEmpty: false,
  concurrent: true,
  configPath: './path/to/configuration/file',
  cwd: process.cwd(),
  debug: false,
  maxArgLength: null,
  quiet: false,
  relative: false,
  shell: false
  stash: true,
  verbose: false
})

const success = await lintStaged({
  allowEmpty: false,
  concurrent: true,
  config: { '*.js': 'eslint --fix' },
  cwd: process.cwd(),
  debug: false,
  maxArgLength: null,
  quiet: false,
  relative: false,
  shell: false,
  stash: true,
  verbose: false,
})

Using with JetBrains IDEs (WebStorm, PyCharm, IntelliJ IDEA, RubyMine, etc.)

{
  "husky": {
    "hooks": {
      "pre-commit": "lint-staged",
      "post-commit": "git update-index --again"
    }
  }
}

{
  "scripts": {
    "precommit": "lint-staged",
    "postcommit": "git update-index --again"
  }
}

How to use lint-staged in a multi-package monorepo?

// ./.lintstagedrc.json
{ "*.md": "prettier --write" }

// ./packages/frontend/.lintstagedrc.json
{ "*.js": "eslint --fix" }

import baseConfig from '../.lintstagedrc.js'

export default {
  ...baseConfig,
  '*.js': 'eslint --fix',
}

Can I lint files outside of the current project folder?

How can I ignore files from .eslintignore?

import { CLIEngine } from 'eslint'

export default {
  '*.js': (files) => {
    const cli = new CLIEngine({})
    return 'eslint --max-warnings=0 ' + files.filter((file) => !cli.isPathIgnored(file)).join(' ')
  },
}

import { ESLint } from 'eslint'

const removeIgnoredFiles = async (files) => {
  const eslint = new ESLint()
  const isIgnored = await Promise.all(
    files.map((file) => {
      return eslint.isPathIgnored(file)
    })
  )
  const filteredFiles = files.filter((_, i) => !isIgnored[i])
  return filteredFiles.join(' ')
}

export default {
  '**/*.{ts,tsx,js,jsx}': async (files) => {
    const filesToLint = await removeIgnoredFiles(files)
    return [`eslint --max-warnings=0 ${filesToLint}`]
  },
}