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Configure Plugins & Parsers

You can extend ESLint with plugins in a variety of different ways. Plugins can include:

  • Custom rules to validate if your code meets a certain expectation, and what to do if it does not meet that expectation.
  • Custom configurations.
  • Custom environments.
  • Custom processors to extract JavaScript code from other kinds of files or preprocess code before linting.

You can also use custom parsers to convert JavaScript code into an abstract syntax tree for ESLint to evaluate. You might want to add a custom parser if your code isn’t compatible with ESLint’s default parser, Espree.

Configure Plugins

ESLint supports the use of third-party plugins. Before using a 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 loads 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 both non-scoped and scoped packages.

A non-scoped package:

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

A scoped package:

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

Use a plugin

Rules, environments, and configurations defined in plugins must be referenced with the following convention:

  • eslint-plugin-foofoo/a-rule
  • @foo/eslint-plugin@foo/a-config
  • @foo/eslint-plugin-bar@foo/bar/a-environment

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,
    }
    // ...
}

Specify a Processor

Plugins may provide processors. Processors can extract JavaScript code from other kinds of files, then let ESLint lint the JavaScript code. Alternatively, processors can convert JavaScript code during preprocessing.

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 the 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 add an overrides entry if you want to lint named code blocks other than *.js.

Configure a Parser

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

  1. It must be a Node module loadable from the config file where the parser is used. 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 works correctly with ESLint. ESLint does 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 that 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.