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

npm install --save-dev lint-staged # requires further setup

$ 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...

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.

• 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!

To install lint-staged in the recommended way, you need to:

1. Install lint-staged itself:
   • npm install --save-dev lint-staged
2. Set up the pre-commit git hook to run lint-staged
   • Husky is a popular choice for configuring git hooks
   • Read more about git hooks here
3. Install some linters, like ESLint or Prettier
4. Configure lint-staged to run linters and other tasks:
   • for example: { "*.js": "eslint" } to run ESLint for all staged JS files
   • See Configuration for more info

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.

See Releases.

• Since v15.0.0 lint-staged no longer supports Node.js 16. Please upgrade your Node.js version to at least 18.12.0.

• Since v14.0.0 lint-staged no longer supports Node.js 14. Please upgrade your Node.js version to at least 16.14.0.

• Since v13.0.0 lint-staged no longer supports Node.js 12. Please upgrade your Node.js version to at least 14.13.1, or 16.0.0 onward.
• Version v13.3.0 was incorrectly released including code of version v14.0.0. This means the breaking changes of v14 are also included in v13.3.0, the last v13 version released

• 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.

• 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.

❯ 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)
  --diff [string]                    override the default "--staged" flag of "git diff" to get list of files. Implies
                                     "--no-stash".
  --diff-filter [string]             override the default "--diff-filter=ACMR" flag of "git diff" to get list of files
  --max-arg-length [number]          maximum length of the command-line argument string (default: 0)
  --no-stash                         disable the backup stash, and do not revert in case of errors. Implies
                                     "--no-hide-partially-staged".
  --no-hide-partially-staged         disable hiding unstaged changes from partially staged files
  -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 listr2; this causes serial, uncoloured output to the terminal, instead of the default (beautified, dynamic) output. (the verbose renderer can also be activated by setting the TERM=dumb or NODE_ENV=test environment variables)
• --diff: By default linters are filtered against all files staged in git, generated from git diff --staged. This option allows you to override the --staged flag with arbitrary revisions. For example to get a list of changed files between two branches, use --diff="branch1...branch2". You can also read more from about git diff and gitrevisions. This option also implies --no-stash.
• --diff-filter: By default only files that are added, copied, modified, or renamed are included. Use this flag to override the default ACMR value with something else: added (A), copied (C), deleted (D), modified (M), renamed (R), type changed (T), unmerged (U), unknown (X), or pairing broken (B). See also the git diff docs for --diff-filter.
• --max-arg-length: long commands (a lot of files) are automatically split into multiple chunks when it detects the current shell cannot handle them. Use this flag to override the maximum length of the generated command string.
• --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. Can be re-enabled with --stash. This option also implies --no-hide-partially-staged.
• --no-hide-partially-staged: By default, unstaged changes from partially staged files will be hidden. This option will disable this behavior and include all unstaged changes in partially staged files. Can be re-enabled with --hide-partially-staged
• --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.

Lint-staged can be configured in many ways:

• lint-staged object in your package.json, or package.yaml
• .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.

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

{
  "*": "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

By default lint-staged will run configured tasks concurrently. This means that for every glob, all the commands will be started at the same time. With the following config, both eslint and prettier will run at the same time:

{
  "*.ts": "eslint",
  "*.md": "prettier --list-different"
}

This is typically not a problem since the globs do not overlap, and the commands do not make changes to the files, but only report possible errors (aborting the git commit). If you want to run multiple commands for the same set of files, you can use the array syntax to make sure commands are run in order. In the following example, prettier will run for both globs, and in addition eslint will run for *.ts files after it. Both sets of commands (for each glob) are still started at the same time (but do not overlap).

{
  "*.ts": ["prettier --list-different", "eslint"],
  "*.md": "prettier --list-different"
}

Pay extra attention when the configured globs overlap, and tasks make edits to files. For example, in this configuration prettier and eslint might try to make changes to the same *.ts file at the same time, causing a race condition:

{
  "*": "prettier --write",
  "*.ts": "eslint --fix"
}

You can solve it using the negation pattern and the array syntax:

{
  "!(*.ts)": "prettier --write",
  "*.ts": ["eslint --fix", "prettier --write"]
}

Another example in which tasks make edits to files and globs match multiple files but don't overlap:

{
  "*.css": [
    "stylelint --fix",
    "prettier --write"
  ],
  "*.{js,jsx}": [
    "eslint --fix",
    "prettier --write"
  ],
  "!(*.css|*.js|*.jsx)": [
    "prettier --write"
  ]
}

Or, if necessary, you can limit the concurrency using --concurrent <number> or disable it entirely with --concurrent false.

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
  • "!(*.css|*.js)" will match all files except CSS and JS files
• 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 /foo directory, so /foo/bar/test.js but 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?

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.

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.

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.

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.

The function can also be async:

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

// 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(' ')}`]
}

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

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

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

// 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(' ')}`]
  },
}

// 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(' ')}`
  },
}

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(' ')}`
  },
}

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.

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.

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

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

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

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

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

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

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

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

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

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

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

// .lintstagedrc.js
// See https://nextjs.org/docs/basic-features/eslint#lint-staged for details

const path = require('path')

const buildEslintCommand = (filenames) =>
  `next lint --fix --file ${filenames.map((f) => path.relative(process.cwd(), f)).join(' --file ')}`

module.exports = {
  '*.{js,jsx,ts,tsx}': [buildEslintCommand],
}

# .husky/pre-commit

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

if sh -c ": >/dev/tty" >/dev/null 2>/dev/null; then exec >/dev/tty 2>&1; fi

npx lint-staged

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,
})

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

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

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

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

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

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

git diff --diff-filter=ACMR --name-only master...my-branch

npx lint-staged --diff="master...my-branch"

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}`]
  },
}

{
  "*.js": "eslint --max-warnings=0 --no-warn-ignored"
}