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Rslint

    file-extension-in-import

    Unreleased

    Configuration

    rslint.config.ts
    import { defineConfig } from '@rslint/core';

export default defineConfig([
  {
    plugins: ['node'],
    rules: {
      'node/file-extension-in-import': 'error',
    },
  },
]);

    Enforce file extension styles in imports and re-exports.

    The rule checks relative and absolute paths in import, export ... from, and literal import() expressions. Package imports, Node builtins, URLs, require() calls, and computed import expressions are ignored.

    Options

    The first option is "always" (the default) or "never". The second option overrides the style for individual target file extensions.

    import { defineConfig } from '@rslint/core';

export default defineConfig([
  {
    plugins: ['node'],
    rules: {
      'node/file-extension-in-import': ['error', 'always', { '.json': 'never' }],
    },
  },
]);

    With "always", an import resolving to helper.js needs its extension:

    // Incorrect
import helper from './helper';
export * from './helper';

// Correct
import helper from './helper.js';
export * from './helper.js';

    With "never", the same file is imported as ./helper. Removing an extension is only fixed automatically when there is one matching entry in its directory. For example, if both helper.js and helper.json exist, the rule reports the extension without removing it.

    Directory imports with an index file are expanded by "always": ./helpers becomes ./helpers/index.js. If several extensions exist, the rule follows settings.node.tryExtensions order, then falls back to the first directory entry. The default search order is .js, .json, .node, .mjs, .cjs.

    TypeScript imports use the emitted extension, such as .js for .ts and .mjs for .mts. Overrides in the second option match the source file extension, before this conversion. The rule reads the nearest TypeScript configuration, including jsx and allowImportingTsExtensions.

    Shared settings.node supports tryExtensions, resolvePaths, tsconfigPath, and typescriptExtensionMap. The latter accepts extension pairs such as [['.ts', '.js'], ['.tsx', '.jsx']], or the presets preserve, react, react-jsx, react-jsxdev, and react-native. An explicit extension map takes precedence over TypeScript configuration. Relative lookup paths use the process working directory.

    Differences from upstream

    For "never", rslint removes the extension while preserving escapes elsewhere in the path. For example, import './\u0061.js' becomes import './\u0061'; upstream can remove the wrong characters from the escaped spelling.

    Queries, fragments, and loader suffixes are preserved separately from the extension. For example, import './a?raw' becomes import './a.js?raw', and import './a!loader' becomes import './a.js!loader'. With "never", import './a.js?raw' becomes import './a?raw'. Upstream can append the extension after a suffix or remove the query along with the extension.

    Automatic fixes also leave non-string import() arguments unchanged. If a custom extension contains a backslash, line break, or the string's quote delimiter, the rule reports it without inserting it verbatim. For example, mapping .ts to .x'js does not automatically modify import './a.ts', which would otherwise produce invalid JavaScript.

    On Unix, directory imports whose names contain literal backslashes are not expanded. For example, if a directory named a\b contains index.js, upstream expands import './a\\b' to import './a\\b/index.js'; rslint leaves this JavaScript import unchanged. Use directory names without literal backslashes. In TypeScript, a missing-extension diagnostic may still be reported, but no extension is added automatically when the path cannot be checked reliably.

    References