Enforce file extension in import

.changeset/four-cooks-bow.md

@@ -0,0 +1,12 @@
+---
+'@cloudfour/eslint-plugin': major
+---
+
+Enabled [`@cloudfour/n/file-extension-in-import`](https://github.com/weiran-zsd/eslint-plugin-node/blob/HEAD/docs/rules/file-extension-in-import.md).
+
+❌ `require('./foo')` → ✅ `require('./foo.js')`
+❌ `import * as foo from './foo'` → ✅ `import * as foo from './foo.js'`
+
+If the file that you are importing is a `.ts` file, you must import it as `.js`, because of a [decision that the TypeScript team made](https://github.com/microsoft/TypeScript/issues/16577#issuecomment-754941937).
+
+It is auto-fixable.

fixtures/downshift/src/hooks/useCombobox/reducer.js

@@ -1,4 +1,4 @@
-import { getHighlightedIndexOnOpen, getDefaultValue } from '../utils';
+import { getHighlightedIndexOnOpen, getDefaultValue } from '../utils.js';
 import { getNextWrappingIndex, getNextNonDisabledIndex } from '../../utils';
 import * as stateChangeTypes from './stateChangeTypes';
 

fixtures/downshift/src/hooks/useCombobox/utils.js

@@ -4,7 +4,7 @@ import {
   getElementIds as getElementIdsCommon,
   defaultProps as defaultPropsCommon,
   getInitialState as getInitialStateCommon,
-} from '../utils';
+} from '../utils.js';
 
 function getElementIds({ id, inputId, ...rest }) {
   const uniqueId = id === undefined ? `downshift-${generateId()}` : id;

fixtures/downshift/src/hooks/useSelect/reducer.js

@@ -1,6 +1,6 @@
 import { getNextWrappingIndex, getNextNonDisabledIndex } from '../../utils';
-import { getHighlightedIndexOnOpen, getDefaultValue } from '../utils';
-import { getItemIndexByCharacterKey } from './utils';
+import { getHighlightedIndexOnOpen, getDefaultValue } from '../utils.js';
+import { getItemIndexByCharacterKey } from './utils.js';
 import * as stateChangeTypes from './stateChangeTypes';
 
 /* eslint-disable complexity */

fixtures/downshift/src/hooks/useSelect/utils.js

@@ -1,5 +1,5 @@
 import PropTypes from 'prop-types';
-import { defaultProps as commonDefaultProps } from '../utils';
+import { defaultProps as commonDefaultProps } from '../utils.js';
 
 // eslint-disable-next-line max-params
 function getItemIndexByCharacterKey(

fixtures/rollup/rollup.config.js

@@ -11,7 +11,7 @@ import addCliEntry from './build-plugins/add-cli-entry.js';
 import conditionalFsEventsImport from './build-plugins/conditional-fsevents-import';
 import emitModulePackageFile from './build-plugins/emit-module-package-file.js';
 import esmDynamicImport from './build-plugins/esm-dynamic-import.js';
-import getLicenseHandler from './build-plugins/generate-license-file';
+import getLicenseHandler from './build-plugins/generate-license-file.js';
 import pkg from './package.json';
 
 const commitHash = (function () {

package.json

@@ -35,7 +35,7 @@
     "@typescript-eslint/parser": "^5.0.0",
     "eslint-plugin-import": "^2.25.4",
     "eslint-plugin-jsdoc": "^39.0.0",
-    "eslint-plugin-n": "^15.0.1",
+    "eslint-plugin-n": "^15.2.1",
     "eslint-plugin-promise": "^6.0.0",
     "eslint-plugin-unicorn": "^42.0.0"
   },

src/config.js

@@ -143,6 +143,7 @@ module.exports.configs = {
         'n/no-unsupported-features/es-syntax': 'off', // Does not account for transpilation
         'n/no-unpublished-require': 'off', // Does not account for "build" scripts
         'n/shebang': 'off', // Tons of false positives
+        'n/file-extension-in-import': ['error', 'always'], // Don't allow extension-less relative imports (e.g. use ./foo.js instead of ./foo)
 
         'unicorn/import-style': 'off', // It doesn't seem useful to force people to use named, default, or namespace imports
         'unicorn/prevent-abbreviations': 'off', // Causes more issues than it's worth