Eeslint

eslint/v8-to-v9

Migrate ESLint configuration from v8 to v9 flat config format

transformationmigrationeslintv8v9
Private
11 executions
Apply to Repository

Run locally

npx codemod @eslint/v8-to-v9

@eslint/v8-to-v9

Automatically migrate your ESLint configuration from v8 to v9 flat config format.

Overview

This codemod provides a comprehensive migration solution for ESLint v8 to v9:

  • Config Migration: Converts .eslintrc.* files to the new flat config format
  • Breaking Changes: Handles all v9 breaking changes in rules and options
  • JSDoc Migration: Migrates deprecated JSDoc rules to eslint-plugin-jsdoc
  • Comment Cleanup: Fixes malformed comments and removes deprecated syntax

What This Codemod Does

This codemod performs a comprehensive migration from ESLint v8 to v9. It handles the following breaking changes from the official ESLint v9 migration guide:

  • ✅ New default config format (eslint.config.js)
  • ✅ Removed require-jsdoc and valid-jsdoc rules - migrates to eslint-plugin-jsdoc
  • ✅ Multiple /* eslint */ comments for the same rule are now disallowed - removes duplicates
  • ✅ Stricter /* exported */ parsing - fixes malformed comments
  • ✅ no-constructor-return and no-sequences rule schemas are stricter - updates to new format
  • ✅ no-restricted-imports now accepts multiple config entries with the same name - deduplicates paths
  • ✅ "eslint:recommended" and "eslint:all" no longer accepted in flat config - converts to js.configs.*
  • ✅ no-unused-vars now defaults caughtErrors to "all" - adds backward-compatible default
  • ✅ no-useless-computed-key flags unnecessary computed member names in classes by default - adds enforceForClassMembers: false
  • ✅ camelcase allow option only accepts an array of strings - validates and migrates options
  • ✅ Linter now expects flat config format - generates flat config files

Detailed Transformations:

1. Configuration File Migration

  • Converts .eslintrc.js, .eslintrc.json, .eslintrc.yaml, and .eslintrc.yml to the new flat config format (eslint.config.cjs)
  • Transforms extends configurations (e.g., "eslint:recommended" → js.configs.recommended)
  • Migrates env settings to the new languageOptions.globals format
  • Updates globals and parserOptions to the flat config structure
  • Preserves overrides by converting them to separate configuration objects
  • Adds necessary imports (@eslint/js, globals, etc.)

2. Rule Transformations

Automatically updates several ESLint rules with breaking changes:

  • no-unused-vars: Adds default caughtErrors: 'none' option
  • no-useless-computed-key: Adds enforceForClassMembers: false option
  • no-sequences: Properly migrates allowInParentheses option
  • no-constructor-return: Ensures proper array format
  • camelcase: Migrates options while handling complex allow patterns
  • no-restricted-imports: Restructures paths configuration

3. JSDoc Migration

  • Detects require-jsdoc and valid-jsdoc rules (removed in ESLint v9)
  • Migrates to eslint-plugin-jsdoc with appropriate configuration
  • Removes deprecated JSDoc-related eslint comments

4. Comment Cleanup

  • Removes unnecessary eslint comments from files
  • Fixes malformed /* exported */ comments to proper format

Usage

Simply run the codemod in your project directory. It will automatically find and migrate all .eslintrc.* files:

bash

Manual Steps Required

After running this codemod, you may need to:

  1. Install new dependencies:
bash

  1. Update JSDoc settings manually if needed (marked with // TODO: Migrate settings manually)

  2. Test your ESLint configuration:

bash

What Gets Transformed

Before (.eslintrc.json)

json

After (eslint.config.cjs)

javascript

Resources

Official ESLint Documentation

Ready to contribute?

Build your own codemod and share it with the community.

Publish a codemodJoin the community