Lint Fn

2.45.0 verified Fri May 01 auth: no javascript

lint-fn is a Node.js library (v2.45.0) that runs ESLint with automatic fixes using predefined rules based on file path. It supports JavaScript and TypeScript files, has a peer dependency on TypeScript 4.7.4, and requires Node.js >15. Differentiators include file-path-based rule selection and environment variable support for skipping specific ESLint rules. The package ships TypeScript types, but has a known issue with linting certain TypeScript declaration files like rambda/files/index.d.ts. Development appears slow, with a TODO item referencing lack of ESLint debug config. The library is published on npm and hosted on GitHub under selfrefactor/services.

Common errors

error Error [ERR_REQUIRE_ESM]: require() of ES Module /path/to/lint-fn/index.js from /path/to/your-file.js not supported. ↓

cause Using CommonJS require() to import an ESM-only module with Node.js <15 or without module type.

fix

Use dynamic import: import('lint-fn') or switch to ES modules.

error TypeError: lintFn is not a function ↓

cause Attempting default import without default export, or mixing named and default imports incorrectly.

fix

Use import lintFn from 'lint-fn' for default, or import { lintFn } for named.

error Cannot find module 'typescript' or its corresponding type declarations. ↓

cause TypeScript peer dependency not installed.

fix

npm install typescript@4.7.4 --save-dev

Warnings

breaking Version 2.0+ is ESM-only and requires Node.js >15. CommonJS require() will fail. ↓

fix Use import syntax or upgrade to Node.js >15 and set 'type': 'module' in package.json.

deprecated Default import may be removed in future versions; prefer named import { lintFn } for clarity. ↓

fix Switch to import { lintFn } from 'lint-fn'.

gotcha Linting of TypeScript declaration files (*.d.ts) may not work correctly; manual ESLint debug config needed. ↓

fix Add ESLint debug configuration or avoid linting .d.ts files directly.

gotcha Predefined rules depend on file path; custom rules may be overridden if not passed correctly. ↓

fix Ensure custom rules are passed in the options object; check documentation for path-based rule precedence.

Install

npm install lint-fn

yarn add lint-fn

pnpm add lint-fn

Imports

default
wrong
```
const lintFn = require('lint-fn')
```
correct
```
import lintFn from 'lint-fn'
```
ESM-only since v2. The default export is a function that lints a file.
lintFn
```
import { lintFn } from 'lint-fn'
```
Named export for the lint function. Both default and named exports exist.
type LintOptions
wrong
```
import { LintOptions } from 'lint-fn'
```
correct
```
import type { LintOptions } from 'lint-fn'
```
Type import for TypeScript types. Use 'import type' to avoid runtime overhead.

Quickstart

Demonstrates importing lintFn and using it to lint a TypeScript file with custom rules and env variable to skip a rule.

import lintFn from 'lint-fn';

const filePath = 'src/index.ts';
const options = {
  fix: true,
  rules: {
    'no-unused-vars': 'error'
  },
  // SKIP_ESLINT_RULES env var can skip rules: 'no-nested-ternary, max-len'
};

process.env.SKIP_ESLINT_RULES = 'no-nested-ternary';

lintFn(filePath, options)
  .then((result) => {
    console.log('Lint fixed:', result);
  })
  .catch((error) => {
    console.error('Lint error:', error);
  });