lobehub/.agents/skills/vercel-react-best-practices/rules/bundle-barrel-imports.md
Innei fcdaf9d814 🔧 chore: update eslint v2 configuration and suppressions (#12133)
* v2 init

* chore: update eslint suppressions and package dependencies

- Removed several eslint suppressions related to array sorting and reversing from eslint-suppressions.json to clean up the configuration.
- Updated @lobehub/lint package version from 2.0.0-beta.6 to 2.0.0-beta.7 in package.json for improvements and bug fixes.
- Made minor formatting adjustments in vitest.config.mts and various SKILL.md files for better readability and consistency.

Signed-off-by: Innei <tukon479@gmail.com>

* fix: clean up import statements and formatting

- Removed unnecessary whitespace in replaceComponentImports.ts for improved readability.
- Standardized import statements in contextEngineering.ts and createAgentExecutors.ts by adding missing spaces for consistency.

Signed-off-by: Innei <tukon479@gmail.com>

* chore: update eslint suppressions and clean up code formatting

* 🐛 fix: use vi.hoisted for mock variable initialization

Fix TDZ error in persona service test by using vi.hoisted() to ensure
mock variables are available when vi.mock factory runs.

---------

Signed-off-by: Innei <tukon479@gmail.com>
2026-02-11 13:04:48 +08:00

2.3 KiB

title impact impactDescription tags
Avoid Barrel File Imports CRITICAL 200-800ms import cost, slow builds bundle, imports, tree-shaking, barrel-files, performance

Avoid Barrel File Imports

Import directly from source files instead of barrel files to avoid loading thousands of unused modules. Barrel files are entry points that re-export multiple modules (e.g., index.js that does export * from './module').

Popular icon and component libraries can have up to 10,000 re-exports in their entry file. For many React packages, it takes 200-800ms just to import them, affecting both development speed and production cold starts.

Why tree-shaking doesn't help: When a library is marked as external (not bundled), the bundler can't optimize it. If you bundle it to enable tree-shaking, builds become substantially slower analyzing the entire module graph.

Incorrect (imports entire library):

import { Check, X, Menu } from 'lucide-react';
// Loads 1,583 modules, takes ~2.8s extra in dev
// Runtime cost: 200-800ms on every cold start

import { Button, TextField } from '@mui/material';
// Loads 2,225 modules, takes ~4.2s extra in dev

Correct (imports only what you need):

import Check from 'lucide-react/dist/esm/icons/check';
import X from 'lucide-react/dist/esm/icons/x';
import Menu from 'lucide-react/dist/esm/icons/menu';
// Loads only 3 modules (~2KB vs ~1MB)

import Button from '@mui/material/Button';
import TextField from '@mui/material/TextField';
// Loads only what you use

Alternative (Next.js 13.5+):

// next.config.js - use optimizePackageImports
module.exports = {
  experimental: {
    optimizePackageImports: ['lucide-react', '@mui/material'],
  },
};

// Then you can keep the ergonomic barrel imports:
import { Check, X, Menu } from 'lucide-react';
// Automatically transformed to direct imports at build time

Direct imports provide 15-70% faster dev boot, 28% faster builds, 40% faster cold starts, and significantly faster HMR.

Libraries commonly affected: lucide-react, @mui/material, @mui/icons-material, @tabler/icons-react, react-icons, @headlessui/react, @radix-ui/react-*, lodash, ramda, date-fns, rxjs, react-use.

Reference: How we optimized package imports in Next.js