eslint-plugin-import

What is eslint-plugin-import?

The eslint-plugin-import npm package is a plugin for ESLint that provides linting functionality for ES2015+ (ES6+) import/export syntax, and helps prevent issues with misspelling of file paths and import names, as well as other common mistakes in import declaration.

What are eslint-plugin-import's main functionalities?

Static analysis

This feature checks for modules that are imported but cannot be resolved to a file in the file system. It helps in catching typos or incorrect paths in import statements.

"rules": { "import/no-unresolved": "error" }

Helpful warnings

This feature ensures that named imports correspond to a named export in the remote file. It prevents importing names that do not exist in the exported module.

"rules": { "import/named": "error" }

Style guide enforcement

This feature enforces a convention in module import order, making the code more readable and organized by ensuring a consistent order of imports.

"rules": { "import/order": "error" }

Preventing issues

This feature prevents exporting mutable bindings which can create hard to follow bugs due to their values being changed by other modules.

"rules": { "import/no-mutable-exports": "error" }

Forbidding certain imports

This feature allows you to restrict which files can be imported in a given folder, helping to enforce separation of concerns within your codebase.

"rules": { "import/no-restricted-paths": "error" }

Other packages similar to eslint-plugin-import

eslint-plugin-node

This package provides similar linting rules for Node.js specific features and best practices. It includes rules that prevent issues related to file paths and imports, but is more focused on Node.js environment compatibility.

eslint-plugin-modules

This is another plugin that focuses on linting ECMAScript 2015+ module syntax. However, it is not as widely used or as comprehensive as eslint-plugin-import.

eslint-plugin-requirejs

This plugin is designed for linting RequireJS import syntax. It is similar in that it helps with module import issues, but it is specific to the RequireJS AMD module loader, whereas eslint-plugin-import is for ES2015+ module syntax.

README

eslint-plugin-import

This plugin intends to support linting of ES2015+ (ES6+) import/export syntax, and prevent issues with misspelling of file paths and import names. All the goodness that the ES2015+ static module syntax intends to provide, marked up in your editor.

IF YOU ARE USING THIS WITH SUBLIME: see the bottom section for important info.

Rules

• Ensure imports point to a file/module that can be resolved. (no-unresolved)
• Ensure named imports correspond to a named export in the remote file. (named)
• Ensure a default export is present, given a default import. (default)
• Ensure imported namespaces contain dereferenced properties as they are dereferenced. (namespace)
• Report any invalid exports, i.e. re-export of the same name (export)

Helpful warnings:

• Report CommonJS require calls. (no-require)
• Report use of exported name as identifier of default export (no-named-as-default)
• Report repeated import of the same module in multiple places (no-duplicates, warning by default)

Style rules:

• Ensure all imports appear before other statements (imports-first)

Installation

npm install eslint-plugin-import -g

or if you manage ESLint as a dev dependency:

# inside your project's working tree
npm install eslint-plugin-import --save-dev

As of v0.9, all rules are off by default. However, you may configure them manually in your .eslintrc, or extend one of the canned base configs from the eslint-config-import package:

---
extends:
  - "eslint:recommended"
  - import/warnings  # after `npm i -D eslint-config-import`-ing

# or configure manually:
plugins:
  - import

rules:
  import/no-unresolved: [2, {commonjs: true, amd: true}]
  import/named: 2
  import/namespace: 2
  import/default: 2
  import/export: 2
  # etc...

Rule Details

no-unresolved

Ensures an imported module can be resolved to a module on the local filesystem, as defined by standard Node require.resolve behavior.

See settings for customization options for the resolution (i.e. additional filetypes, NODE_PATH, etc.)

This rule can also optionally report on unresolved modules in CommonJS require('./foo') calls and AMD require(['./foo'], function (foo){...}) and define(['./foo'], function (foo){...}).

To enable this, send { commonjs: true/false, amd: true/false } as a rule option. Both are disabled by default.

If you are using Webpack, see the section on resolver plugins.

named

Verifies that all named imports are part of the set of named exports in the referenced module.

For export, verifies that all named exports exist in the referenced module.

default

If a default import is requested, this rule will report if there is no default export in the imported module.

For ES7, reports if a default is named and exported but is not found in the referenced module.

namespace

Enforces names exist at the time they are dereferenced, when imported as a full namespace (i.e. import * as foo from './foo'; foo.bar(); will report if bar is not exported by ./foo.).

Will report at the import declaration if there are no exported names found.

Also, will report for computed references (i.e. foo["bar"]()).

Reports on assignment to a member of an imported namespace.

Implementation note: currently, this rule does not check for possible redefinition of the namespace in an intermediate scope. Adherence to the ESLint no-shadow rule for namespaces will prevent this from being a problem.

For ES7, reports if an exported namespace would be empty (no names exported from the referenced module.)

no-require

Reports require([string]) function calls. Will not report if >1 argument, or single argument is not a literal string.

Intended for temporary use when migrating to pure ES6 modules.

Given:

// ./mod.js
export const foo = 'bar'
export function bar() { return foo }

// ./common.js
exports.something = 'whatever'

This would be reported:

var mod = require('./mod')
  , common = require('./common')
  , fs = require('fs')
  , whateverModule = require('./not-found')

no-named-as-default

Reports use of an exported name as the locally imported name of a default export.

Given:

// foo.js
export default 'foo';
export const bar = 'baz';

...this would be valid:

import foo from './foo.js';

...and this would be reported:

// message: Using exported name 'bar' as identifier for default export.
import bar from './foo.js';

Rationale: using an exported name as the name of the default export is likely...

• misleading: others familiar with foo.js probably expect the name to be foo
• a mistake: only needed to import bar and forgot the brackets (the case that is prompting this)

For ES7, this also prevents exporting the default from a referenced module as a name within than module, for the same reasons:

// valid:
export foo from './foo.js'

// message: Using exported name 'bar' as identifier for default export.
export bar from './foo.js';

export

Reports funny business with exports, such as

export default class MyClass { /*...*/ } // Multiple default exports.

function makeClass() { return new MyClass(...arguments) }

export default makeClass // Multiple default exports.

or

export const foo = function () { /*...*/ } // Multiple exports of name 'foo'.

function bar() { /*...*/ }
export { bar as foo } // Multiple exports of name 'foo'.

In the case of named/default re-export, all n re-exports will be reported, as at least n-1 of them are clearly mistakes, but it is not clear which one (if any) is intended. Could be the result of copy/paste, code duplication with intent to rename, etc.

no-duplicates

Reports if a resolved path is imported more than once.

Valid:

import SomeDefaultClass, * as names from './mod'

...whereas here, both ./mod imports will be reported:

import SomeDefaultClass from './mod'

// oops, some other import separated these lines
import foo from './some-other-mod'

import * as names from './mod'

The motivation is that this is likely a result of two developers importing different names from the same module at different times (and potentially largely different locations in the file.) This rule brings both (or n-many) to attention.

This rule is only set to a warning, by default.

imports-first

By popular demand, this rule reports any imports that come after non-import statments:

import foo from './foo'

// some module-level initializer
initWith(foo)

import bar from './bar' // <- reported

Providing absolute-first as an option will report any absolute imports (i.e. packages) that come after any relative imports:

import foo from 'foo'
import bar from './bar'

import * as _ from 'lodash' // <- reported

This rule is disabled by default.

Resolver plugins

With the advent of module bundlers and the current state of modules and module syntax specs, it's not always obvious where import x from 'module' should look to find the file behind module.

Up through v0.10ish, this plugin has directly used substack's resolve plugin, which implements Node's import behavior. This works pretty well in most cases.

However, Webpack allows a number of things in import module source strings that Node does not, such as loaders (import 'file!./whatever') and a number of aliasing schemes, such as externals: mapping a module id to a global name at runtime (allowing some modules to be included more traditionally via script tags).

In the interest of supporting both of these, v0.11 introduces resolver plugins. At the moment, these are modules exporting a single function:

exports.resolveImport = function (source, file, config) {
  // return source's absolute path given
  // - file: absolute path of importing module
  // - config: optional config provided for this resolver

  // return `null` if source is a "core" module (i.e. "fs", "crypto") that
  // can't be found on the filesystem
}

The default node plugin that uses resolve is a handful of lines:

var resolve = require('resolve')
  , path = require('path')
  , assign = require('object-assign')

exports.resolveImport = function resolveImport(source, file, config) {
  if (resolve.isCore(source)) return null

  return resolve.sync(source, opts(path.dirname(file), config))
}

function opts(basedir, config) {
  return assign( {}
               , config
               , { basedir: basedir }
               )
}

It essentially just uses the current file to get a reference base directory (basedir) and then passes through any explicit config from the .eslintrc; things like non-standard file extensions, module directories, etc.

Currently Node and Webpack resolution have been implemented, but the resolvers are just npm packages, so third party packages are supported (and encouraged!).

Just install a resolver as eslint-import-resolver-foo and reference it as such:

settings:
  import/resolver: foo

or with a config object:

settings:
  import/resolver:
    foo: { someConfigKey: value }

Settings

You may set the following settings in your .eslintrc:

import/ignore

A list of regex strings that, if matched by a path, will not parse the matching module. In practice, this means rules other than no-unresolved will not report on the import in question.

import/resolver

See resolver plugins.

import/parser

This setting allows you to provide a custom parser module, in the event your project uses syntax not understood by Babel.

This plugin defaults to using Babylon, Babel's internal parser, but is also compatible with Espree's AST. As long as the import nodes follow ESTree, any parser should work.

If you're using babel-eslint as ESLint's parser, you probably don't need to specify it here (anymore, as of v0.9).

import/parse-options

This setting will be merged 1-level deep (think Object.assign) with the default parse options and passed as the second parameter to the parser: parse(file, options). See the import/es7-jsx config file for an example of explicit parse options for Babylon.

Or, if you are using another parser, you may want to set these options as well. (and maybe contribute another config file! i.e. eslint-config-import/espree)

Here is an example .eslintrc for reference:

extends:
  - "eslint:recommended"
  - import/warnings  # optionally start from eslint-config-import

# if not using the `extends` package, make sure to add the plugin here:
plugins:
  - import

rules:
  import/default: 2
  import/no-unresolved: 1

settings:

  import/ignore:
    # any imported module path matching one of these patterns will not be parsed
    - 'node_modules' # this is the default, but must be included if overwritten
    - '\\.es5$'

  import/resolver: webpack # will use 'node' if not specified

  import/parser: esprima-fb  # default is 'babylon'. change if needed.

SublimeLinter-eslint

Recently, SublimeLinter-eslint introduced a change to support .eslintignore files which altered the way file paths are passed to ESLint when linting during editing.

See roadhump/SublimeLinter-eslint#58 for more details, but essentially, you may find you need to add the following to a .sublimelinterrc file:

{
  "linters": {
    "eslint": {
      "args": ["--stdin-filename", "@"]
    }
  }
}

I also found that I needed to set rc_search_limit to null, which removes the file hierarchy search limit when looking up the directory tree for .sublimelinterrc:

In Package Settings / SublimeLinter / User Settings:

{
  "user": {
    "rc_search_limit": null
  }
}

I believe this defaults to 3, so you may not need to alter it depending on your project folder max depth.

Changelog

[0.11.0] - 2015-11-27

Added

• Resolver plugins. Now the linter can read Webpack config, properly follow aliases and ignore externals, dismisses inline loaders, etc. etc.!