extensions.md

import/extensions

Some file resolve algorithms allow you to omit the file extension within the import source path. For example the node resolver (which does not yet support ESM/import) can resolve ./foo/bar to the absolute path /User/someone/foo/bar.js because the .js extension is resolved automatically by default in CJS. Depending on the resolver you can configure more extensions to get resolved automatically.

In order to provide a consistent use of file extensions across your code base, this rule can enforce or disallow the use of certain file extensions.

Rule Details

This rule either takes one string option, one object option, or a string and an object option. If it is the string "never" (the default value), then the rule forbids the use for any extension. If it is the string "always", then the rule enforces the use of extensions for all import statements. If it is the string "ignorePackages", then the rule enforces the use of extensions for all import statements except package imports.

"import/extensions": [<severity>, "never" | "always" | "ignorePackages"]

By providing an object you can configure each extension separately.

"import/extensions": [<severity>, {
  <extension>: "never" | "always" | "ignorePackages"
}]

For example { "js": "always", "json": "never" } would always enforce the use of the .js extension but never allow the use of the .json extension.

By providing both a string and an object, the string will set the default setting for all extensions, and the object can be used to set granular overrides for specific extensions.

"import/extensions": [
  <severity>,
  "never" | "always" | "ignorePackages",
  {
    <extension>: "never" | "always" | "ignorePackages"
  }
]

For example, ["error", "never", { "svg": "always" }] would require that all extensions are omitted, except for "svg".

ignorePackages can be set as a separate boolean option like this:

"import/extensions": [
  <severity>,
  "never" | "always" | "ignorePackages",
  {
    ignorePackages: true | false,
    pattern: {
      <extension>: "never" | "always" | "ignorePackages"
    }
  }
]

In that case, if you still want to specify extensions, you can do so inside the pattern property. Default value of ignorePackages is false.

By default, import type and export type style imports/exports are ignored. If you want to check them as well, you can set the checkTypeImports option to true.

Unfortunately, in more advanced linting setups, such as when employing custom specifier aliases (e.g. you're using eslint-import-resolver-alias, paths in tsconfig.json, etc), this rule can be too coarse-grained when determining which imports to ignore and on which to enforce the config. This is especially troublesome if you have import specifiers that look like externals or builtins.

Set pathGroupOverrides to force this rule to always ignore certain imports and never ignore others. pathGroupOverrides accepts an array of one or more PathGroupOverride objects.

For example:

"import/extensions": [
  <severity>,
  "never" | "always" | "ignorePackages",
  {
    ignorePackages: true | false,
    pattern: {
      <extension>: "never" | "always" | "ignorePackages"
    },
    pathGroupOverrides: [
      {
        pattern: "package-name-to-ignore",
        action: "ignore",
      },
      {
        pattern: "bespoke+alias:{*,*/**}",
        action: "enforce",
      }
    ]
  }
]

Note

pathGroupOverrides is inspired by pathGroups in 'import/order' and shares a similar interface. If you're using pathGroups already, you may find pathGroupOverrides very useful.

PathGroupOverride

property	required	type	description
pattern	☑️	string	Minimatch pattern for specifier matching
patternOptions		object	Minimatch options; default: {nocomment: true}
action	☑️	"enforce" | "ignore"	What action to take on imports whose specifiers match pattern

Exception

When disallowing the use of certain extensions this rule makes an exception and allows the use of extension when the file would not be resolvable without extension.

For example, given the following folder structure:

├── foo
│   ├── bar.js
│   ├── bar.json

and this import statement:

import bar from './foo/bar.json';

then the extension can’t be omitted because it would then resolve to ./foo/bar.js.

Examples

The following patterns are considered problems when configuration set to "never":

import foo from './foo.js';

import bar from './bar.json';

import Component from './Component.jsx';

import express from 'express/index.js';

The following patterns are not considered problems when configuration set to "never":

import foo from './foo';

import bar from './bar';

import Component from './Component';

import express from 'express/index';

import * as path from 'path';

The following patterns are considered problems when the configuration is set to "never" and the option "checkTypeImports" is set to true:

import type { Foo } from './foo.ts';

export type { Foo } from './foo.ts';

The following patterns are considered problems when configuration set to "always":

import foo from './foo';

import bar from './bar';

import Component from './Component';

import foo from '@/foo';

The following patterns are not considered problems when configuration set to "always":

import foo from './foo.js';

import bar from './bar.json';

import Component from './Component.jsx';

import * as path from 'path';

import foo from '@/foo.js';

The following patterns are considered problems when configuration set to "ignorePackages":

import foo from './foo';

import bar from './bar';

import Component from './Component';

The following patterns are not considered problems when configuration set to "ignorePackages":

import foo from './foo.js';

import bar from './bar.json';

import Component from './Component.jsx';

import express from 'express';

import foo from '@/foo'

The following patterns are not considered problems when configuration set to ['error', 'always', {ignorePackages: true} ]:

import Component from './Component.jsx';

import baz from 'foo/baz.js';

import express from 'express';

import foo from '@/foo';

The following patterns are considered problems when the configuration is set to "always" and the option "checkTypeImports" is set to true:

import type { Foo } from './foo';

export type { Foo } from './foo';

When Not To Use It

If you are not concerned about a consistent usage of file extension.

In the future, when this rule supports native node ESM resolution, and the plugin is configured to use native rather than transpiled ESM (a config option that is not yet available) - setting this to always will have no effect.