chore(deps): FE-454 Update to ESLint 9 #298

PascalZajac · 2025-10-20T20:56:58Z

What & Why?

Migrate from ESLint 8 to ESLint 9 with the new flat config format.

BREAKING CHANGE: This package now requires ESLint 9.x

Why ESLint 9?

ESLint 8 reaches end-of-life
Flat config is simpler and more explicit
Better TypeScript integration
Improved performance

📖 Review Guide

TL;DR: Focus on configs/*.js and index.js. Skip the snapshots.

🟢 Skip These (~14K lines)

Files	Why Skip
`*.snap` files	Auto-generated, format change only
`yarn.lock`	Dependency lockfile

💡 Tip: Add *.snap to GitHub's file filter to hide them:

Click "Files changed" tab
Click the gear icon ⚙️
Add *.snap to "File filter"

🔴 Focus Review Here (~1.3K lines)

Files	What Changed
`configs/base.js`	Core rules → flat config format
`configs/typescript.js`	TS rules → flat config format
`configs/react.js`	React rules → flat config format
`index.js`	Entry point, conditional config loading
`utils/index.js`	`hasPackage()` helper

🟡 Glance At (~300 lines)

Files	What Changed
`test/*.spec.js`	Updated for new ESLint API
`README.md`	Usage instructions updated
`package.json`	`"type": "module"`, peer deps

Changes Summary

Config Structure

- module.exports = { extends: ['...'], rules: {...} }
+ export default [{ rules: {...} }, ...]

ES Modules

- const foo = require('foo');
- module.exports = { ... };
+ import foo from 'foo';
+ export default [...];

Entry Point

- module.exports = { extends: [...] }
+ export default (async () => {
+   const configs = [...baseConfig];
+   if (await hasPackage('react')) configs.push(...reactConfig);
+   return configs;
+ })();

Examples

Before (ESLint 8)

// .eslintrc.js
require('@bigcommerce/eslint-config/patch');

module.exports = {
  extends: ['@bigcommerce/eslint-config'],
};

After (ESLint 9)

// eslint.config.js
import eslintConfig from '@bigcommerce/eslint-config';

export default [...(await eslintConfig)];

Testing

✅ All 28 tests passing
✅ Lint clean
✅ Verified in store-control-panel#3915

packages/eslint-config/README.md

packages/eslint-config/configs/typescript.js

Copilot

Pull Request Overview

This PR updates the repository to support ESLint 9 with its new flat config format, replacing the legacy ESLint 8 configuration system. The migration includes converting all modules to ES modules ("type": "module"), replacing CommonJS with ES module syntax, and restructuring configuration files to use the flat config format.

Key Changes:

Updated ESLint peer dependency from ^8.0.0 to ^9.0.0 across all packages
Converted all configuration files from CommonJS to ES modules
Restructured ESLint configs to use flat config format instead of the legacy .eslintrc format

Reviewed Changes

Copilot reviewed 33 out of 41 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
package.json	Updated ESLint to 9.x, added module type, modified test script for ES modules
packages/eslint-plugin/package.json	Updated ESLint peer dependency to 9.x and added module type
packages/eslint-config/package.json	Updated ESLint peer dependency to 9.x, added module type, replaced patch dependency with @eslint/js and globals
packages/eslint-plugin/index.js	Converted to ES modules with flat config format for plugin configuration
packages/eslint-plugin/rules/jsx-short-circuit-conditionals.js	Converted to ES modules and removed deprecated config properties
packages/eslint-plugin/tests/jsx-short-circuit-conditionals.spec.js	Converted to ES modules with compatibility handling for default exports
packages/eslint-config/index.js	Converted to async ES module returning flat config array
packages/eslint-config/configs/*.js	Converted all config files to ES modules with flat config format
packages/eslint-config/utils/index.js	Converted to async ES module using dynamic imports
packages/eslint-config/test/*.spec.js	Updated test files to ES modules with proper async handling
packages/eslint-config/prettier.config.js	Converted to ES module export
packages/eslint-config/jest.config.js	Added transform config for ES modules
eslint.config.js	New flat config file replacing .eslintrc.js
README.md	Updated documentation for ESLint 9 migration

Comments suppressed due to low confidence (1)

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

packages/eslint-plugin/rules/jsx-short-circuit-conditionals.js

packages/eslint-config/utils/index.js

packages/eslint-config/test/__snapshots__/tsx.spec.js.snap

oliverdowie · 2025-10-29T03:57:22Z

Any estimate on when this upgrade will be available? I'm currently converting our Catalyst project to Nextjs 16 and ESLint 9 but getting a little stuck on the BigCommerce configs.
Thanks :)

PascalZajac · 2025-10-31T08:13:03Z

@oliverdowie thanks for the question! It actually helps to know there are other people out there interested / waiting on this. We'll aim to get it finalised next week.

BREAKING CHANGE: This package now requires ESLint 9.x ## Summary - Convert all configs to ESLint 9 flat config format - Convert from CommonJS to ES modules - Update peer dependency from eslint@^8.0.0 to eslint@^9.0.0 ## Changes by Category ### Config Structure (configs/*.js) - Restructured all config files to use flat config array format - Replaced 'extends' with spread operator imports - Updated plugin references to use new naming convention ### ES Modules Conversion - Added "type": "module" to package.json files - Replaced require() with import statements - Replaced module.exports with export default ### Entry Point (index.js) - Now exports async config array - Conditionally includes configs based on installed packages ### Tests - Updated test utilities for new ESLint API - Regenerated snapshots with new format ### Dependencies - Bump lerna ^8.1.2 → ^8.1.8 - Bump typescript ^5.0.2 → ^5.6.3 Addresses Copilot review comments: - Fix 'Disallows' → 'Disallow' in rule description - Remove redundant schema comment - Clarify hasPackage() implementation comment

icatalina · 2026-01-15T10:15:57Z

hey @danielochoa-epam , can you please rebase instead of merging master into here?

PascalZajac force-pushed the FE-454 branch from 9627d49 to 60a2125 Compare October 20, 2025 21:04

PascalZajac commented Oct 20, 2025

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PascalZajac requested a review from Copilot October 20, 2025 21:26

Copilot AI reviewed Oct 20, 2025

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icatalina reviewed Oct 21, 2025

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PascalZajac force-pushed the FE-454 branch 3 times, most recently from 71d0856 to 6940e6a Compare October 22, 2025 23:31

PascalZajac force-pushed the FE-454 branch from 30d8f73 to c82be5b Compare December 3, 2025 21:25

PascalZajac marked this pull request as ready for review December 3, 2025 21:27

danielochoa-epam force-pushed the FE-454 branch from a78549a to fb8a65e Compare January 14, 2026 17:07

danielochoa-epam force-pushed the FE-454 branch from fb8a65e to 6bc5d91 Compare January 14, 2026 17:11

chore: merge master into FE-454

de14ba8

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chore(deps): FE-454 Update to ESLint 9 #298

chore(deps): FE-454 Update to ESLint 9 #298

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PascalZajac commented Oct 20, 2025 •

edited by danielochoa-epam

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What & Why?

Why ESLint 9?

📖 Review Guide

🟢 Skip These (~14K lines)

🔴 Focus Review Here (~1.3K lines)

🟡 Glance At (~300 lines)

Changes Summary

Config Structure

ES Modules

Entry Point

Examples

Before (ESLint 8)

After (ESLint 9)

Testing

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Pull Request Overview

Reviewed Changes

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oliverdowie commented Oct 29, 2025

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PascalZajac commented Oct 20, 2025 •

edited by danielochoa-epam

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