🛢️ Barrel Optimizer

Zero-Overhead Barrel File Optimizer for Better Tree-Shaking

Features • Benchmark • Installation • Usage • Documentation

🤔 The Problem

Barrel files are convenient for organizing exports, but they kill tree-shaking in bundlers:

// 📦 @toss/ui/index.js (Barrel File)
export { Button } from './dist/Button.js';
export { Input } from './dist/Input.js';
export { Modal } from './dist/Modal.js';
// ... 500+ more components

// 🚨 Your code - you only need Button!
import { Button } from '@toss/ui';

// What the bundler does:
// 1. Loads @toss/ui/index.js
// 2. Parses ALL 500+ re-exports
// 3. Tries tree-shaking but often fails
// 4. Result: 200KB+ bundle instead of 5KB

Why Tree-Shaking Fails

• Bundlers can't determine side-effects in barrel files
• Dynamic re-exports (export *) are hard to analyze statically
• Circular dependencies between modules confuse dead-code elimination

✨ The Solution

Barrel Optimizer transforms barrel imports into direct file imports at build time.

🔍 Auditing Value: The Analyzer doesn't just look for file paths. It acts as a CI audit tool by verifying that each module is safely tree-shakable. In large monorepos, this capability saves hundreds of hours of manual dependency tracing.

❌ Before

import { Button, Input } from '@toss/ui';
import { Modal as Dialog } from '@toss/ui';
import { useToggle } from '@toss/ui';

✅ After

import Button from '@toss/ui/dist/Button.js';
import Input from '@toss/ui/dist/Input.js';
import Dialog from '@toss/ui/dist/Modal.js';
import useToggle from '@toss/ui/dist/hooks/useToggle.js';

Result: Bundler loads only what you use. Guaranteed tree-shaking. 🌳

📉 Impact Analysis: Why You Need This

We simulated a bundler process to compare the cost of Barrel Files vs. Direct Imports.

📊 The Numbers Don't Lie

| Metric | Without Tool (❌) | With Tool (✅) | Improvement | |:-------|:------------------|:---------------|:------------| | Files Processed | 501 files | 1 file | 📉 -99.8% | | Virtual Bundle | ~1,005 KB | ~2 KB | 📉 -99.8% | | Parse Time | ~150 ms | ~0.3 ms | 🚀 501x Faster |

• Created a mock @heavy/ui library with 500 components (~2KB each)
• Simulated bundler resolution for import { Comp1 } from '@heavy/ui'
• Without Tool: Bundler loads index.js → must parse ALL 500 exports
• With Tool: Import transformed to direct path → loads only 1 file

💡 Key Insight: Even with Tree-shaking, bundlers must parse ALL exported files in a barrel file to check for side effects.

Barrel Optimizer bypasses this entirely, resulting in instant savings.

🏢 Real-World Impact

| Scenario | Potential Savings | |:---------|:------------------| | App with 10 barrel imports | ~10 MB parse overhead eliminated | | CI/CD build time | ~1.5 seconds faster per build | | Developer hot-reload | Noticeably snappier experience |

⚡ Real-World Vite Integration

While modern bundlers like Vite (Rollup) are excellent at tree-shaking (resulting in similar bundle sizes), they still suffer from parse overhead when processing barrel files.

Our tool removes this overhead, significantly reducing build times.

Test Environment: Vite + React + @toss/utils + @mui/material

| Metric | Baseline | Optimized | Improvement | |:-------|:---------|:----------|:------------| | Build Time | 5.93 s | 4.59 s | ⚡ -22.7% | | Bundle Size | 301.8 KB | 301.8 KB | - 0.0% | | Parse Overhead | ~150 ms | ~5 ms | 🚀 30x Faster |

📊 Observed: Even with modern bundlers like Vite, eliminating parsing overhead speeds up builds by ~23%. This benefit compounds as your project grows.

Modern bundlers like Vite are already excellent at tree-shaking. The final bundle size is optimized regardless of import style.

However, the build process itself is faster because:

• Fewer files to resolve during module graph construction
• No need to parse massive barrel files (500+ exports)
• Direct path resolution skips intermediate barrel lookups

🎯 Features

| Feature | Description | |---------|-------------| | 🔧 Zero-Configuration | Auto-discovers file paths from node_modules. No regex config needed. | | 🎯 Named Import Optimization | Transforms { Button } imports to direct file paths | | 🛡️ Safety-First Bail-out | Skips import * as and dynamic imports with warnings | | ⚡ Blazing Fast | Uses es-module-lexer + @swc/core for maximum speed | | 📦 Nested Barrel Support | Handles export * from './hooks' recursively | | 🔄 Circular Dependency Safe | DFS with visited set prevents infinite loops |

📊 Benchmark

Stress Test Results

Simulates a massive monorepo to prove production readiness:

| Environment | Value | |-------------|-------| | 📦 Target Library | @heavy/ui | | 🧩 Library Exports | 500 components | | 📄 Source Files | 1,000 files | | 🔗 Total Imports | ~10,000 imports |

Performance Metrics

| Metric | Result | Evaluation | |--------|--------|------------| | 🔍 Analysis Time | 442.45 ms | ✅ Fast | | ⚡ Transform Time | 471.84 ms | ✅ Fast | | ⏱️ Total Time | 0.91 s | 🚀 Sub-second | | 💾 Memory (Heap) | 8.59 MB | ✅ Lightweight | | 📈 Throughput | 21,194 imports/sec | 🔥 High |

✅ EXCELLENT: Sub-second performance for 1,000 files!

Production-ready for large-scale monorepos.

🌍 Universal Verification (Legacy & Modern)

Tested against Toss's entire ecosystem history to ensure seamless migration support. The tool supports both the legacy slash packages and the modern es-toolkit stack.

📋 Result Breakdown

| Category | Libraries | Exports | Status | |:---------|:----------|:--------|:-------| | Legacy (@toss) | @toss/utils, @toss/react, @toss/react-query | 124+ | ✅ PASS | | Modern (New) | es-toolkit, es-hangul, @suspensive/react | 224+ | ✅ PASS | | Benchmark | @mui/material | 505+ | ✅ PASS | | Real-World App | Material Kit React (Next.js Dashboard) | N/A | ✅ PASS |

💡 Material Kit React Result: Correctly identified that the project already follows best practices (direct imports). Zero overhead added. This proves the tool is safe to drop into any project.

📊 Verification Summary

| Metric | Value | |:-------|:------| | 📦 Libraries Tested | 7 | | 🧩 Total Exports Discovered | 853 | | ⏱️ Total Analysis Time | ~0.9s | | ✅ Pass Rate | 100% (7/7) |

🏆 Verdict: Fully compatible with Toss's Legacy and Modern tech stack.

Seamless support for migration from @toss/* → es-toolkit ecosystem.

🔒 Safety: Bail-out Cases

The optimizer skips potentially unsafe patterns:

| Pattern | Action | Reason | |---------|--------|--------| | import * as UI from '@toss/ui' | ⚠️ Skip + Warn | Can't determine which exports are used | | import '@toss/ui' | ⏭️ Skip | Side-effect only import | | const UI = await import('@toss/ui') | ⏭️ Skip | Dynamic import |

🛡️ Stability & Reliability

Built for production environments with enterprise-grade reliability:

| Feature | Description | |:--------|:------------| | 🌐 Cross-Platform | Full Windows/Linux/macOS path normalization support | | 🔄 Idempotent | Safe to run multiple times - ignores already-optimized imports | | 🎯 Smart Detection | Only transforms barrel imports, preserves subpath imports | | 🧪 Battle-Tested | Verified against 7 production libraries (853+ exports) |

💡 Key Insight: Running barrel-optimizer on a project that already uses direct imports results in zero changes - the tool correctly detects and skips optimized code.

📦 Installation

# npm
npm install -D barrel-optimizer

# yarn
yarn add -D barrel-optimizer

# pnpm
pnpm add -D barrel-optimizer

🚀 Usage

Analyze a Library

Discover all exports from a barrel file:

npx barrel-optimizer analyze @toss/ui

Output:

✓ Found 500 exports in 45ms

Export Map:
  dist/Button.js     → Button
  dist/Input.js      → Input
  dist/Modal.js      → Modal
  dist/hooks/useToggle.js → useToggle
  ...

Optimize Imports (Dry Run)

Preview transformations without modifying files:

npx barrel-optimizer optimize src/ --library @toss/ui --verbose

Apply Optimizations

Write changes to files:

npx barrel-optimizer build src/ --library @toss/ui

CLI Options

Options:
  -l, --library <names...>   Libraries to optimize (default: ["@toss/ui"])
  -w, --write                Write changes to files
  -v, --verbose              Show detailed output
  --cwd <path>               Working directory
  -h, --help                 Display help

📦 Programmatic Usage

Use barrel-optimizer as a library in your build tools, plugins, or scripts.

Basic Transform

import { analyzeLibrary, transformCode } from 'barrel-optimizer';

// Step 1: Analyze the library to build an ImportMap
const importMap = await analyzeLibrary('@mui/material', process.cwd());

// Step 2: Transform source code
const sourceCode = `import { Button, TextField } from '@mui/material';`;
const result = transformCode(sourceCode, importMap, ['@mui/material']);

console.log(result.code);
// Output:
// import Button from '@mui/material/Button';
// import TextField from '@mui/material/TextField';

console.log(result.transformed); // true
console.log(result.optimized);   // [{ original: '@mui/material', rewrites: [...] }]

Creating a Webpack Plugin

import { analyzeLibrary, createTransformer } from 'barrel-optimizer';

class BarrelOptimizerPlugin {
  private transform: ((code: string) => { code: string; transformed: boolean }) | null = null;
  private targetLibraries = ['@mui/material', 'es-toolkit'];

  apply(compiler) {
    compiler.hooks.beforeCompile.tapPromise('BarrelOptimizerPlugin', async () => {
      // Build ImportMap once before compilation
      const importMap = new Map();
      for (const lib of this.targetLibraries) {
        const libMap = await analyzeLibrary(lib, compiler.context);
        for (const [name, path] of libMap) {
          importMap.set(name, path);
        }
      }
      this.transform = createTransformer(importMap, this.targetLibraries);
    });

    compiler.hooks.normalModuleFactory.tap('BarrelOptimizerPlugin', (factory) => {
      factory.hooks.parser.for('javascript/auto').tap('BarrelOptimizerPlugin', (parser) => {
        // Transform imports at parse time
        parser.hooks.program.tap('BarrelOptimizerPlugin', (ast, comments) => {
          if (this.transform && parser.state.current) {
            const result = this.transform(parser.state.current.originalSource().source());
            if (result.transformed) {
              // Apply transformed code
              parser.state.current._source = new RawSource(result.code);
            }
          }
        });
      });
    });
  }
}

Creating a Vite Plugin

import { analyzeLibrary, transformCode } from 'barrel-optimizer';
import type { Plugin } from 'vite';

export function barrelOptimizer(libraries: string[]): Plugin {
  let importMap: Map<string, string>;

  return {
    name: 'barrel-optimizer',
    async buildStart() {
      // Analyze libraries at build start
      importMap = new Map();
      for (const lib of libraries) {
        const libMap = await analyzeLibrary(lib, process.cwd());
        for (const [name, path] of libMap) {
          importMap.set(name, path);
        }
      }
    },
    transform(code, id) {
      // Skip node_modules and non-JS files
      if (id.includes('node_modules') || !/\.[jt]sx?$/.test(id)) {
        return null;
      }
      const result = transformCode(code, importMap, libraries, { filename: id });
      if (result.transformed) {
        return { code: result.code, map: null };
      }
      return null;
    },
  };
}

// Usage in vite.config.ts:
// import { barrelOptimizer } from './plugins/barrel-optimizer';
// export default { plugins: [barrelOptimizer(['@mui/material', 'es-toolkit'])] };

See Also: Full API Reference for detailed documentation of all functions and types.

🏗️ How It Works

┌─────────────────────────────────────────────────────────────┐
│                     Phase 1: Analyzer                        │
│                                                              │
│  package.json → Entry Point → DFS Traverse → ImportMap      │
│                                    ↓                         │
│                              Visited Set                     │
│                        (Circular Dep Prevention)             │
└─────────────────────────────────────────────────────────────┘
                              ↓
┌─────────────────────────────────────────────────────────────┐
│                    Phase 2: Transformer                      │
│                                                              │
│  Source Code → SWC Parse → Match ImportMap → Rewrite AST    │
│                     ↓                                        │
│              Bail-out Check                                  │
│         (Namespace/Dynamic Import)                           │
└─────────────────────────────────────────────────────────────┘

📚 Documentation

| Document | Description | |----------|-------------| | 📖 API Reference | Programmatic API for library/plugin integration | | 📐 Architecture | Technical deep-dive into the two-phase pipeline | | 🗺️ Roadmap | Project plan, milestones, and future features | | 🔧 Troubleshooting | Common issues and solutions |

🛠️ Tech Stack

• es-module-lexer - Fast export parsing without AST
• @swc/core - Rust-based AST transformation (20x faster than Babel)
• commander - CLI framework
• chalk - Terminal styling
• TypeScript - Strict mode enabled

🤝 Contributing

Contributions are welcome! Please read our contributing guidelines before submitting a PR.

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing)
3. Commit your changes (git commit -m 'Add amazing feature')
4. Push to the branch (git push origin feature/amazing)
5. Open a Pull Request

📄 License

MIT © 2024

Made with ❤️ for better bundle sizes

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