Configuring ESLint

ESLint is designed to be completely configurable, meaning you can turn off every rule and run only with basic syntax validation, or mix and match the bundled rules and your custom rules to make ESLint perfect for your project. There are two primary ways to configure ESLint:

  1. Configuration Comments - use JavaScript comments to embed configuration information directly into a file.
  2. Configuration Files - use a JavaScript, JSON or YAML file to specify configuration information for an entire directory and all of its subdirectories. This can be in the form of an .eslintrc.* file or an eslintConfig field in a package.json file, both of which ESLint will look for and read automatically, or you can specify a configuration file on the command line.

There are several pieces of information that can be configured:

All of these options give you fine-grained control over how ESLint treats your code.

Table of Contents

Specifying Parser Options

ESLint allows you to specify the JavaScript language options you want to support. By default, ESLint expects ECMAScript 5 syntax. You can override that setting to enable support for other ECMAScript versions as well as JSX by using parser options.

Please note that supporting JSX syntax is not the same as supporting React. React applies specific semantics to JSX syntax that ESLint doesn't recognize. We recommend using eslint-plugin-react if you are using React and want React semantics. By the same token, supporting ES6 syntax is not the same as supporting new ES6 globals (e.g., new types such as Set). For ES6 syntax, use { "parserOptions": { "ecmaVersion": 6 } }; for new ES6 global variables, use { "env": { "es6": true } }. { "env": { "es6": true } } enables ES6 syntax automatically, but { "parserOptions": { "ecmaVersion": 6 } } does not enable ES6 globals automatically. Parser options are set in your .eslintrc.* file by using the parserOptions property. The available options are:

Here's an example .eslintrc.json file:

{
    "parserOptions": {
        "ecmaVersion": 6,
        "sourceType": "module",
        "ecmaFeatures": {
            "jsx": true
        }
    },
    "rules": {
        "semi": "error"
    }
}

Setting parser options helps ESLint determine what is a parsing error. All language options are false by default.

Specifying Parser

By default, ESLint uses Espree as its parser. You can optionally specify that a different parser should be used in your configuration file so long as the parser meets the following requirements:

  1. It must be a Node module loadable from the config file where it appears. Usually, this means you should install the parser package separately using npm.
  2. It must conform to the parser interface.

Note that even with these compatibilities, there are no guarantees that an external parser will work correctly with ESLint and ESLint will not fix bugs related to incompatibilities with other parsers.

To indicate the npm module to use as your parser, specify it using the parser option in your .eslintrc file. For example, the following specifies to use Esprima instead of Espree:

{
    "parser": "esprima",
    "rules": {
        "semi": "error"
    }
}

The following parsers are compatible with ESLint:

Note when using a custom parser, the parserOptions configuration property is still required for ESLint to work properly with features not in ECMAScript 5 by default. Parsers are all passed parserOptions and may or may not use them to determine which features to enable.

Specifying Processor

Plugins may provide processors. Processors can extract JavaScript code from another kind of files, then lets ESLint lint the JavaScript code. Or processors can convert JavaScript code in preprocessing for some purpose.

To specify processors in a configuration file, use the processor key with the concatenated string of a plugin name and a processor name by a slash. For example, the following enables the processor a-processor that the plugin a-plugin provided:

{
    "plugins": ["a-plugin"],
    "processor": "a-plugin/a-processor"
}

To specify processors for specific kinds of files, use the combination of the overrides key and the processor key. For example, the following uses the processor a-plugin/markdown for *.md files.

{
    "plugins": ["a-plugin"],
    "overrides": [
        {
            "files": ["*.md"],
            "processor": "a-plugin/markdown"
        }
    ]
}

Processors may make named code blocks such as 0.js and 1.js. ESLint handles such a named code block as a child file of the original file. You can specify additional configurations for named code blocks in the overrides section of the config. For example, the following disables strict rule for the named code blocks which end with .js in markdown files.

{
    "plugins": ["a-plugin"],
    "overrides": [
        {
            "files": ["*.md"],
            "processor": "a-plugin/markdown"
        },
        {
            "files": ["**/*.md/*.js"],
            "rules": {
                "strict": "off"
            }
        }
    ]
}

ESLint checks the file path of named code blocks then ignores those if any overrides entry didn't match the file path. Be sure to make overrides entry if you wanted to lint named code blocks other than *.js.

Specifying Environments

An environment defines global variables that are predefined. The available environments are:

These environments are not mutually exclusive, so you can define more than one at a time.

Environments can be specified inside of a file, in configuration files or using the --env command line flag.

To specify environments using a comment inside of your JavaScript file, use the following format:

/* eslint-env node, mocha */

This enables Node.js and Mocha environments.

To specify environments in a configuration file, use the env key and specify which environments you want to enable by setting each to true. For example, the following enables the browser and Node.js environments:

{
    "env": {
        "browser": true,
        "node": true
    }
}

Or in a package.json file

{
    "name": "mypackage",
    "version": "0.0.1",
    "eslintConfig": {
        "env": {
            "browser": true,
            "node": true
        }
    }
}

And in YAML:

---
  env:
    browser: true
    node: true

If you want to use an environment from a plugin, be sure to specify the plugin name in the plugins array and then use the unprefixed plugin name, followed by a slash, followed by the environment name. For example:

{
    "plugins": ["example"],
    "env": {
        "example/custom": true
    }
}

Or in a package.json file

{
    "name": "mypackage",
    "version": "0.0.1",
    "eslintConfig": {
        "plugins": ["example"],
        "env": {
            "example/custom": true
        }
    }
}

And in YAML:

---
  plugins:
    - example
  env:
    example/custom: true

Specifying Globals

The no-undef rule will warn on variables that are accessed but not defined within the same file. If you are using global variables inside of a file then it's worthwhile to define those globals so that ESLint will not warn about their usage. You can define global variables either using comments inside of a file or in the configuration file.

To specify globals using a comment inside of your JavaScript file, use the following format:

/* global var1, var2 */

This defines two global variables, var1 and var2. If you want to optionally specify that these global variables can be written to (rather than only being read), then you can set each with a "writable" flag:

/* global var1:writable, var2:writable */

To configure global variables inside of a configuration file, set the globals configuration property to an object containing keys named for each of the global variables you want to use. For each global variable key, set the corresponding value equal to "writable" to allow the variable to be overwritten or "readonly" to disallow overwriting. For example:

{
    "globals": {
        "var1": "writable",
        "var2": "readonly"
    }
}

And in YAML:

---
  globals:
    var1: writable
    var2: readonly

These examples allow var1 to be overwritten in your code, but disallow it for var2.

Globals can be disabled with the string "off". For example, in an environment where most ES2015 globals are available but Promise is unavailable, you might use this config:

{
    "env": {
        "es6": true
    },
    "globals": {
        "Promise": "off"
    }
}

For historical reasons, the boolean value false and the string value "readable" are equivalent to "readonly". Similarly, the boolean value true and the string value "writeable" are equivalent to "writable". However, the use of older values is deprecated.

Note: Enable the no-global-assign rule to disallow modifications to read-only global variables in your code.

Configuring Plugins

ESLint supports the use of third-party plugins. Before using the plugin, you have to install it using npm.

To configure plugins inside of a configuration file, use the plugins key, which contains a list of plugin names. The eslint-plugin- prefix can be omitted from the plugin name.

{
    "plugins": [
        "plugin1",
        "eslint-plugin-plugin2"
    ]
}

And in YAML:

---
  plugins:
    - plugin1
    - eslint-plugin-plugin2

Notes:

  1. Plugins are resolved relative to the config file. In other words, ESLint will load the plugin as a user would obtain by running require('eslint-plugin-pluginname') in the config file.
  2. Plugins in the base configuration (loaded by extends setting) are relative to the derived config file. For example, if ./.eslintrc has extends: ["foo"] and the eslint-config-foo has plugins: ["bar"], ESLint finds the eslint-plugin-bar from ./node_modules/ (rather than ./node_modules/eslint-config-foo/node_modules/) or ancestor directories. Thus every plugin in the config file and base configurations is resolved uniquely.

Naming Convention

Include a Plugin

The eslint-plugin- prefix can be omitted for non-scoped packages

{
    // ...
    "plugins": [
        "jquery", // means eslint-plugin-jquery
    ]
    // ...
}

The same rule does apply to scoped packages:

{
    // ...
    "plugins": [
        "@jquery/jquery", // means @jquery/eslint-plugin-jquery
        "@foobar" // means @foobar/eslint-plugin
    ]
    // ...
}

Use a Plugin

When using rules, environments or configs defined by plugins, they must be referenced following the convention:

For example:

{
    // ...
    "plugins": [
        "jquery",   // eslint-plugin-jquery
        "@foo/foo", // @foo/eslint-plugin-foo
        "@bar"      // @bar/eslint-plugin
    ],
    "extends": [
        "plugin:@foo/foo/recommended",
        "plugin:@bar/recommended"
    ],
    "rules": {
        "jquery/a-rule": "error",
        "@foo/foo/some-rule": "error",
        "@bar/another-rule": "error"
    },
    "env": {
        "jquery/jquery": true,
        "@foo/foo/env-foo": true,
        "@bar/env-bar": true,
    }
    // ...
}

Configuring Rules

ESLint comes with a large number of rules. You can modify which rules your project uses either using configuration comments or configuration files. To change a rule setting, you must set the rule ID equal to one of these values:

Using Configuration Comments

To configure rules inside of a file using configuration comments, use a comment in the following format:

/* eslint eqeqeq: "off", curly: "error" */

In this example, eqeqeq is turned off and curly is turned on as an error. You can also use the numeric equivalent for the rule severity:

/* eslint eqeqeq: 0, curly: 2 */

This example is the same as the last example, only it uses the numeric codes instead of the string values. The eqeqeq rule is off and the curly rule is set to be an error.

If a rule has additional options, you can specify them using array literal syntax, such as:

/* eslint quotes: ["error", "double"], curly: 2 */

This comment specifies the "double" option for the quotes rule. The first item in the array is always the rule severity (number or string).

Configuration comments can include descriptions to explain why the comment is necessary. The description must occur after the configuration and is separated from the configuration by two or more consecutive - characters. For example:

/* eslint eqeqeq: "off", curly: "error" -- Here's a description about why this configuration is necessary. */

/* eslint eqeqeq: "off", curly: "error"
    --------
    Here's a description about why this configuration is necessary. */

/* eslint eqeqeq: "off", curly: "error"
 * --------
 * This will not work due to the line above starting with a '*' character.
 */

Using Configuration Files

To configure rules inside of a configuration file, use the rules key along with an error level and any options you want to use. For example:

{
    "rules": {
        "eqeqeq": "off",
        "curly": "error",
        "quotes": ["error", "double"]
    }
}

And in YAML:

---
rules:
  eqeqeq: off
  curly: error
  quotes:
    - error
    - double

To configure a rule which is defined within a plugin you have to prefix the rule ID with the plugin name and a /. For example:

{
    "plugins": [
        "plugin1"
    ],
    "rules": {
        "eqeqeq": "off",
        "curly": "error",
        "quotes": ["error", "double"],
        "plugin1/rule1": "error"
    }
}

And in YAML:

---
plugins:
  - plugin1
rules:
  eqeqeq: 0
  curly: error
  quotes:
    - error
    - "double"
  plugin1/rule1: error

In these configuration files, the rule plugin1/rule1 comes from the plugin named plugin1. You can also use this format with configuration comments, such as:

/* eslint "plugin1/rule1": "error" */

Note: When specifying rules from plugins, make sure to omit eslint-plugin-. ESLint uses only the unprefixed name internally to locate rules.

Disabling Rules with Inline Comments

To temporarily disable rule warnings in your file, use block comments in the following format:

/* eslint-disable */

alert('foo');

/* eslint-enable */

You can also disable or enable warnings for specific rules:

/* eslint-disable no-alert, no-console */

alert('foo');
console.log('bar');

/* eslint-enable no-alert, no-console */

To disable rule warnings in an entire file, put a /* eslint-disable */ block comment at the top of the file:

/* eslint-disable */

alert('foo');

You can also disable or enable specific rules for an entire file:

/* eslint-disable no-alert */

alert('foo');

To disable all rules on a specific line, use a line or block comment in one of the following formats:

alert('foo'); // eslint-disable-line

// eslint-disable-next-line
alert('foo');

/* eslint-disable-next-line */
alert('foo');

alert('foo'); /* eslint-disable-line */

To disable a specific rule on a specific line:

alert('foo'); // eslint-disable-line no-alert

// eslint-disable-next-line no-alert
alert('foo');

alert('foo'); /* eslint-disable-line no-alert */

/* eslint-disable-next-line no-alert */
alert('foo');

To disable multiple rules on a specific line:

alert('foo'); // eslint-disable-line no-alert, quotes, semi

// eslint-disable-next-line no-alert, quotes, semi
alert('foo');

alert('foo'); /* eslint-disable-line no-alert, quotes, semi */

/* eslint-disable-next-line no-alert, quotes, semi */
alert('foo');

All of the above methods also work for plugin rules. For example, to disable eslint-plugin-example's rule-name rule, combine the plugin's name (example) and the rule's name (rule-name) into example/rule-name:

foo(); // eslint-disable-line example/rule-name
foo(); /* eslint-disable-line example/rule-name */

Configuration comments can include descriptions to explain why the comment is necessary. The description must occur after the configuration and is separated from the configuration by two or more consecutive - characters. For example:

// eslint-disable-next-line no-console -- Here's a description about why this configuration is necessary.
console.log('hello');

Note: Comments that disable warnings for a portion of a file tell ESLint not to report rule violations for the disabled code. ESLint still parses the entire file, however, so disabled code still needs to be syntactically valid JavaScript.

Disabling Rules Only for a Group of Files

To disable rules inside of a configuration file for a group of files, use the overrides key along with a files key. For example:

{
  "rules": {...},
  "overrides": [
    {
      "files": ["*-test.js","*.spec.js"],
      "rules": {
        "no-unused-expressions": "off"
      }
    }
  ]
}

Configuring Inline Comment Behaviors

Disabling Inline Comments

To disable all inline config comments, use noInlineConfig setting. For example:

{
  "rules": {...},
  "noInlineConfig": true
}

This setting is similar to --no-inline-config CLI option.

Report Unused eslint-disable Comments

To report unused eslint-disable comments, use reportUnusedDisableDirectives setting. For example:

{
  "rules": {...},
  "reportUnusedDisableDirectives": true
}

This setting is similar to --report-unused-disable-directives CLI option, but doesn't fail linting (reports as "warn" severity).

Adding Shared Settings

ESLint supports adding shared settings into configuration file. You can add settings object to ESLint configuration file and it will be supplied to every rule that will be executed. This may be useful if you are adding custom rules and want them to have access to the same information and be easily configurable.

In JSON:

{
    "settings": {
        "sharedData": "Hello"
    }
}

And in YAML:

---
  settings:
    sharedData: "Hello"

Using Configuration Files

There are two ways to use configuration files.

The first way to use configuration files is via .eslintrc.* and package.json files. ESLint will automatically look for them in the directory of the file to be linted, and in successive parent directories all the way up to the root directory of the filesystem (unless root: true is specified). This option is useful when you want different configurations for different parts of a project or when you want others to be able to use ESLint directly without needing to remember to pass in the configuration file.

The second is to save the file wherever you would like and pass its location to the CLI using the -c option, such as:

eslint -c myconfig.json myfiletotest.js

If you are using one configuration file and want ESLint to ignore any .eslintrc.* files, make sure to use --no-eslintrc along with the -c flag.

In each case, the settings in the configuration file override default settings.

Configuration File Formats

ESLint supports configuration files in several formats:

If there are multiple configuration files in the same directory, ESLint will only use one. The priority order is:

  1. .eslintrc.js
  2. .eslintrc.cjs
  3. .eslintrc.yaml
  4. .eslintrc.yml
  5. .eslintrc.json
  6. .eslintrc
  7. package.json

Configuration Cascading and Hierarchy

When using .eslintrc.* and package.json files for configuration, you can take advantage of configuration cascading. For instance, suppose you have the following structure:

your-project
├── .eslintrc
├── lib
│ └── source.js
└─┬ tests
  ├── .eslintrc
  └── test.js

The configuration cascade works by using the closest .eslintrc file to the file being linted as the highest priority, then any configuration files in the parent directory, and so on. When you run ESLint on this project, all files in lib/ will use the .eslintrc file at the root of the project as their configuration. When ESLint traverses into the tests/ directory, it will then use your-project/tests/.eslintrc in addition to your-project/.eslintrc. So your-project/tests/test.js is linted based on the combination of the two .eslintrc files in its directory hierarchy, with the closest one taking priority. In this way, you can have project-level ESLint settings and also have directory-specific overrides.

In the same way, if there is a package.json file in the root directory with an eslintConfig field, the configuration it describes will apply to all subdirectories beneath it, but the configuration described by the .eslintrc file in the tests directory will override it where there are conflicting specifications.

your-project
├── package.json
├── lib
│ └── source.js
└─┬ tests
  ├── .eslintrc
  └── test.js

If there is an .eslintrc and a package.json file found in the same directory, .eslintrc will take a priority and package.json file will not be used.

By default, ESLint will look for configuration files in all parent folders up to the root directory. This can be useful if you want all of your projects to follow a certain convention, but can sometimes lead to unexpected results. To limit ESLint to a specific project, place "root": true inside the eslintConfig field of the package.json file or in the .eslintrc.* file at your project's root level. ESLint will stop looking in parent folders once it finds a configuration with "root": true.

{
    "root": true
}

And in YAML:

---
  root: true

For example, consider projectA which has "root": true set in the .eslintrc file in the lib/ directory. In this case, while linting main.js, the configurations within lib/ will be used, but the .eslintrc file in projectA/ will not.

home
└── user
    └── projectA
        ├── .eslintrc  <- Not used
        └── lib
            ├── .eslintrc  <- { "root": true }
            └── main.js

The complete configuration hierarchy, from highest precedence to lowest precedence, is as follows:

  1. Inline configuration
    1. /*eslint-disable*/ and /*eslint-enable*/
    2. /*global*/
    3. /*eslint*/
    4. /*eslint-env*/
  2. Command line options (or CLIEngine equivalents):
    1. --global
    2. --rule
    3. --env
    4. -c, --config
  3. Project-level configuration:
    1. .eslintrc.* or package.json file in same directory as linted file
    2. Continue searching for .eslintrc and package.json files in ancestor directories (parent has highest precedence, then grandparent, etc.), up to and including the root directory or until a config with "root": true is found.

Extending Configuration Files

A configuration file can extend the set of enabled rules from base configurations.

The extends property value is either:

ESLint extends configurations recursively, so a base configuration can also have an extends property. Relative paths and shareable config names in an extends property are resolved from the location of the config file where they appear.

The rules property can do any of the following to extend (or override) the set of rules:

Using "eslint:recommended"

An extends property value "eslint:recommended" enables a subset of core rules that report common problems, which have a check mark on the rules page. The recommended subset can change only at major versions of ESLint.

If your configuration extends the recommended rules: after you upgrade to a newer major version of ESLint, review the reported problems before you use the --fix option on the command line, so you know if a new fixable recommended rule will make changes to the code.

The eslint --init command can create a configuration so you can extend the recommended rules.

Example of a configuration file in JavaScript format:

module.exports = {
    "extends": "eslint:recommended",
    "rules": {
        // enable additional rules
        "indent": ["error", 4],
        "linebreak-style": ["error", "unix"],
        "quotes": ["error", "double"],
        "semi": ["error", "always"],

        // override default options for rules from base configurations
        "comma-dangle": ["error", "always"],
        "no-cond-assign": ["error", "always"],

        // disable rules from base configurations
        "no-console": "off",
    }
}

Using a shareable configuration package

A sharable configuration is an npm package that exports a configuration object. Make sure the package has been installed to a directory where ESLint can require it.

The extends property value can omit the eslint-config- prefix of the package name.

The eslint --init command can create a configuration so you can extend a popular style guide (for example, eslint-config-standard).

Example of a configuration file in YAML format:

extends: standard
rules:
  comma-dangle:
    - error
    - always
  no-empty: warn

Using the configuration from a plugin

A plugin is an npm package that usually exports rules. Some plugins also export one or more named configurations. Make sure the package has been installed to a directory where ESLint can require it.

The plugins property value can omit the eslint-plugin- prefix of the package name.

The extends property value can consist of:

Example of a configuration file in JSON format:

{
    "plugins": [
        "react"
    ],
    "extends": [
        "eslint:recommended",
        "plugin:react/recommended"
    ],
    "rules": {
       "react/no-set-state": "off"
    }
}

Using a configuration file

The extends property value can be an absolute or relative path to a base configuration file. ESLint resolves a relative path to a base configuration file relative to the configuration file that uses it.

Example of a configuration file in JSON format:

{
    "extends": [
        "./node_modules/coding-standard/eslintDefaults.js",
        "./node_modules/coding-standard/.eslintrc-es6",
        "./node_modules/coding-standard/.eslintrc-jsx"
    ],
    "rules": {
        "eqeqeq": "warn"
    }
}

Using "eslint:all"

The extends property value can be "eslint:all" to enable all core rules in the currently installed version of ESLint. The set of core rules can change at any minor or major version of ESLint.

Important: This configuration is not recommended for production use because it changes with every minor and major version of ESLint. Use at your own risk.

If you configure ESLint to automatically enable new rules when you upgrade, ESLint can report new problems when there are no changes to source code, therefore any newer minor version of ESLint can behave as if it has breaking changes.

You might enable all core rules as a shortcut to explore rules and options while you decide on the configuration for a project, especially if you rarely override options or disable rules. The default options for rules are not endorsements by ESLint (for example, the default option for the quotes rule does not mean double quotes are better than single quotes).

If your configuration extends all core rules: after you upgrade to a newer major or minor version of ESLint, review the reported problems before you use the --fix option on the command line, so you know if a new fixable rule will make changes to the code.

Example of a configuration file in JavaScript format:

module.exports = {
    "extends": "eslint:all",
    "rules": {
        // override default options
        "comma-dangle": ["error", "always"],
        "indent": ["error", 2],
        "no-cond-assign": ["error", "always"],

        // disable now, but enable in the future
        "one-var": "off", // ["error", "never"]

        // disable
        "init-declarations": "off",
        "no-console": "off",
        "no-inline-comments": "off",
    }
}

Configuration Based on Glob Patterns

v4.1.0+. Sometimes a more fine-controlled configuration is necessary, for example if the configuration for files within the same directory has to be different. Therefore you can provide configurations under the overrides key that will only apply to files that match specific glob patterns, using the same format you would pass on the command line (e.g., app/**/*.test.js).

How it works

Relative glob patterns

project-root
├── app
│   ├── lib
│   │   ├── foo.js
│   │   ├── fooSpec.js
│   ├── components
│   │   ├── bar.js
│   │   ├── barSpec.js
│   ├── .eslintrc.json
├── server
│   ├── server.js
│   ├── serverSpec.js
├── .eslintrc.json

The config in app/.eslintrc.json defines the glob pattern **/*Spec.js. This pattern is relative to the base directory of app/.eslintrc.json. So, this pattern would match app/lib/fooSpec.js and app/components/barSpec.js but NOT server/serverSpec.js. If you defined the same pattern in the .eslintrc.json file within in the project-root folder, it would match all three of the *Spec files.

If a config is provided via the --config CLI option, the glob patterns in the config are relative to the current working directory rather than the base directory of the given config. For example, if --config configs/.eslintrc.json is present, the glob patterns in the config are relative to . rather than ./configs.

Example configuration

In your .eslintrc.json:

{
  "rules": {
    "quotes": ["error", "double"]
  },

  "overrides": [
    {
      "files": ["bin/*.js", "lib/*.js"],
      "excludedFiles": "*.test.js",
      "rules": {
        "quotes": ["error", "single"]
      }
    }
  ]
}

Specifying Target Files to Lint

If you specified directories with CLI (e.g., eslint lib), ESLint searches target files in the directory to lint. The target files are *.js or the files that match any of overrides entries (but exclude entries that are any of files end with *).

If you specified the --ext command line option along with directories, the target files are only the files that have specified file extensions regardless of overrides entries.

Comments in Configuration Files

Both the JSON and YAML configuration file formats support comments (package.json files should not include them). You can use JavaScript-style comments or YAML-style comments in either type of file and ESLint will safely ignore them. This allows your configuration files to be more human-friendly. For example:

{
    "env": {
        "browser": true
    },
    "rules": {
        // Override our default settings just for this directory
        "eqeqeq": "warn",
        "strict": "off"
    }
}

Ignoring Files and Directories

ignorePatterns in config files

You can tell ESLint to ignore specific files and directories by ignorePatterns in your config files. Each value of ignorePatterns is the same pattern as each line of .eslintignore in the next section.

{
    "ignorePatterns": ["temp.js", "**/vendor/*.js"],
    "rules": {
        //...
    }
}

If a glob pattern starts with /, the pattern is relative to the base directory of the config file. For example, /foo.js in lib/.eslintrc.json matches to lib/foo.js but not lib/subdir/foo.js.

If a config is provided via the --config CLI option, the ignore patterns that start with / in the config are relative to the current working directory rather than the base directory of the given config. For example, if --config configs/.eslintrc.json is present, the ignore patterns in the config are relative to . rather than ./configs.

.eslintignore

You can tell ESLint to ignore specific files and directories by creating an .eslintignore file in your project's root directory. The .eslintignore file is a plain text file where each line is a glob pattern indicating which paths should be omitted from linting. For example, the following will omit all JavaScript files:

**/*.js

When ESLint is run, it looks in the current working directory to find an .eslintignore file before determining which files to lint. If this file is found, then those preferences are applied when traversing directories. Only one .eslintignore file can be used at a time, so .eslintignore files other than the one in the current working directory will not be used.

Globs are matched using node-ignore, so a number of features are available:

Of particular note is that like .gitignore files, all paths used as patterns for both .eslintignore and --ignore-pattern must use forward slashes as their path separators.

# Valid
/root/src/*.js

# Invalid
\root\src\*.js

Please see .gitignore's specification for further examples of valid syntax.

In addition to any patterns in the .eslintignore file, ESLint always follows a couple implicit ignore rules even if the --no-ignore flag is passed. The implicit rules are as follows:

There are also some exceptions to these rules:

Using an Alternate File

If you'd prefer to use a different file than the .eslintignore in the current working directory, you can specify it on the command line using the --ignore-path option. For example, you can use .jshintignore file because it has the same format:

eslint --ignore-path .jshintignore file.js

You can also use your .gitignore file:

eslint --ignore-path .gitignore file.js

Any file that follows the standard ignore file format can be used. Keep in mind that specifying --ignore-path means that any existing .eslintignore file will not be used. Note that globbing rules in .eslintignore follow those of .gitignore.

Using eslintIgnore in package.json

If an .eslintignore file is not found and an alternate file is not specified, ESLint will look in package.json for an eslintIgnore key to check for files to ignore.

{
  "name": "mypackage",
  "version": "0.0.1",
  "eslintConfig": {
      "env": {
          "browser": true,
          "node": true
      }
  },
  "eslintIgnore": ["hello.js", "world.js"]
}

Ignored File Warnings

When you pass directories to ESLint, files and directories are silently ignored. If you pass a specific file to ESLint, then you will see a warning indicating that the file was skipped. For example, suppose you have an .eslintignore file that looks like this:

foo.js

And then you run:

eslint foo.js

You'll see this warning:

foo.js
  0:0  warning  File ignored because of a matching ignore pattern. Use "--no-ignore" to override.

✖ 1 problem (0 errors, 1 warning)

This message occurs because ESLint is unsure if you wanted to actually lint the file or not. As the message indicates, you can use --no-ignore to omit using the ignore rules.

Consider another scenario where you may want to run ESLint on a specific Dotfile or Dotfolder, but have forgotten to specifically allow those files in your .eslintignore file. You would run something like this:

eslint .config/foo.js

You would see this warning:

.config/foo.js
  0:0  warning  File ignored by default.  Use a negated ignore pattern (like "--ignore-pattern '!<relative/path/to/filename>'") to override

✖ 1 problem (0 errors, 1 warning)

This messages occurs because, normally, this file would be ignored by ESLint's implicit ignore rules (as mentioned above). A negated ignore rule in your .eslintignore file would override the implicit rule and reinclude this file for linting. Additionally, in this specific case, --no-ignore could be used to lint the file as well.

Personal Configuration File (deprecated)

⚠️ This feature has been deprecated. This feature will be removed in the 8.0.0 release. If you want to continue to use personal configuration files, please use the --config CLI option. For more information regarding this decision, please see RFC 28 and RFC 32.

~/ refers to the home directory of the current user on your preferred operating system. The personal configuration file being referred to here is ~/.eslintrc.* file, which is currently handled differently than other configuration files.

How ESLint Finds Personal Configuration File

If eslint could not find any configuration file in the project, eslint loads ~/.eslintrc.* file.

If eslint could find configuration files in the project, eslint ignores ~/.eslintrc.* file even if it's in an ancestor directory of the project directory.

How Personal Configuration File Behaves

~/.eslintrc.* files behave similarly to regular configuration files, with some exceptions:

~/.eslintrc.* files load shareable configs and custom parsers from ~/node_modules/ – similarly to require() – in the user's home directory. Please note that it doesn't load global-installed packages.

~/.eslintrc.* files load plugins from $CWD/node_modules by default in order to identify plugins uniquely. If you want to use plugins with ~/.eslintrc.* files, plugins must be installed locally per project. Alternatively, you can use the --resolve-plugins-relative-to CLI option to change the location from which ESLint loads plugins.

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