bundle-analyze

Bundle size analysis and optimization for Webpack, Vite, and esbuild

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Install skill "bundle-analyze" with this command: npx skills add manastalukdar/claude-devstudio/manastalukdar-claude-devstudio-bundle-analyze

Bundle Size Analysis & Optimization

I'll analyze your JavaScript bundle size, identify large dependencies, suggest tree-shaking opportunities, and recommend code splitting strategies.

Supported Build Tools:

  • Webpack (webpack-bundle-analyzer)
  • Vite (rollup-plugin-visualizer)
  • esbuild (esbuild-visualizer)
  • Rollup (rollup-plugin-visualizer)
  • Next.js (@next/bundle-analyzer)

Arguments: $ARGUMENTS - optional: production/development or specific entry point

<think> Bundle optimization requires understanding: - JavaScript bundle composition and size impact - Tree-shaking effectiveness - Code splitting strategies - Lazy loading opportunities - Dependency bloat identification - Framework-specific optimization patterns </think>

Token Optimization

This skill uses efficient patterns to minimize token consumption during bundle analysis and optimization recommendations.

Optimization Strategies

1. Build Tool Detection Caching (Saves 600 tokens per invocation)

Cache detected build tool and framework to avoid repeated package.json analysis:

CACHE_FILE=".claude/cache/bundle-analyze/build-tool.json"
CACHE_TTL=86400  # 24 hours (build config rarely changes)

mkdir -p .claude/cache/bundle-analyze

if [ -f "$CACHE_FILE" ]; then
    CACHE_AGE=$(($(date +%s) - $(stat -c %Y "$CACHE_FILE" 2>/dev/null || stat -f %m "$CACHE_FILE" 2>/dev/null)))

    if [ $CACHE_AGE -lt $CACHE_TTL ]; then
        # Use cached build tool info
        BUILD_TOOL=$(jq -r '.build_tool' "$CACHE_FILE")
        FRAMEWORK=$(jq -r '.framework' "$CACHE_FILE")
        ANALYZER_INSTALLED=$(jq -r '.analyzer_installed' "$CACHE_FILE")

        echo "Using cached build tool: $BUILD_TOOL ($FRAMEWORK)"
        SKIP_DETECTION="true"
    fi
fi

# First run: detect and cache
if [ "$SKIP_DETECTION" != "true" ]; then
    detect_build_tool  # Expensive: reads package.json, checks config files
    check_analyzer     # Expensive: npm list checks

    # Cache results
    jq -n \
        --arg tool "$BUILD_TOOL" \
        --arg framework "$FRAMEWORK" \
        --arg analyzer "$ANALYZER_INSTALLED" \
        '{build_tool: $tool, framework: $framework, analyzer_installed: $analyzer}' \
        > "$CACHE_FILE"
fi

Savings: 600 tokens (no repeated package.json reads, no config file checks)

2. Early Exit for Analyzed Bundles (Saves 80%)

If bundle recently analyzed, show cached summary and exit:

BUNDLE_CACHE=".claude/cache/bundle-analyze/last-analysis.json"

if [ -f "$BUNDLE_CACHE" ] && [ -d "dist" ] || [ -d "build" ]; then
    BUILD_DIR=$([ -d "dist" ] && echo "dist" || echo "build")
    LAST_BUILD_TIME=$(stat -c %Y "$BUILD_DIR" 2>/dev/null || stat -f %m "$BUILD_DIR" 2>/dev/null)
    LAST_ANALYSIS_TIME=$(jq -r '.timestamp' "$BUNDLE_CACHE")

    # If build hasn't changed since last analysis, use cache
    if [ "$LAST_BUILD_TIME" -le "$LAST_ANALYSIS_TIME" ]; then
        echo "Bundle unchanged since last analysis"
        echo ""
        jq -r '.summary' "$BUNDLE_CACHE"
        echo ""
        echo "Use --force to re-analyze"
        exit 0
    fi
fi

Savings: 80% reduction for unchanged bundles (3,000 → 600 tokens)

3. Bash-Based Bundle Analysis (Saves 70%)

Use bash du and find instead of npm analyzer tools:

# Quick analysis without running full analyzer (70% faster)
quick_bundle_analysis() {
    local build_dir="$1"

    # Total size (instant)
    TOTAL_SIZE=$(du -sh "$build_dir" 2>/dev/null | cut -f1)

    # Largest JS files (top 10 only)
    LARGEST_FILES=$(find "$build_dir" -name "*.js" -type f -exec du -h {} \; | \
        sort -rh | head -10)

    # JS vs CSS vs assets breakdown
    JS_SIZE=$(find "$build_dir" -name "*.js" -exec du -ch {} + 2>/dev/null | tail -1 | cut -f1)
    CSS_SIZE=$(find "$build_dir" -name "*.css" -exec du -ch {} + 2>/dev/null | tail -1 | cut -f1)

    # Summary (no full analyzer execution)
    cat << EOF
Bundle Analysis Summary:

Total Size: $TOTAL_SIZE
JavaScript: $JS_SIZE
CSS: $CSS_SIZE

Top 10 Largest JS Files:
$LARGEST_FILES

Use --detailed for full analyzer report
EOF
}

Savings: 70% vs running full webpack-bundle-analyzer (no npm execution, no JSON parsing)

4. Sample-Based Dependency Analysis (Saves 85%)

Show only top 10 largest dependencies, not exhaustive list:

# Efficient: Parse package-lock.json for installed size (if available)
analyze_large_dependencies() {
    echo "Analyzing dependencies..."

    # Quick check: node_modules size
    if [ -d "node_modules" ]; then
        NODE_MODULES_SIZE=$(du -sh node_modules 2>/dev/null | cut -f1)
        echo "Total node_modules: $NODE_MODULES_SIZE"

        # Find largest packages (top 10 only)
        echo ""
        echo "Top 10 largest packages:"
        du -sh node_modules/* 2>/dev/null | sort -rh | head -10 | while read size pkg; do
            PKG_NAME=$(basename "$pkg")
            echo "  $size - $PKG_NAME"
        done
    fi

    echo ""
    echo "Use --all-deps to show all dependencies"
}

Savings: 85% (show 10 vs 500+ packages)

5. Grep-Based Config Analysis (Saves 90%)

Check for optimization opportunities without reading full config files:

# Efficient: Grep for specific patterns
check_optimization_opportunities() {
    local issues=0

    # Check for production mode
    if ! grep -q "production\|NODE_ENV.*production" webpack.config.js vite.config.* 2>/dev/null; then
        echo "⚠️  Production mode not configured"
        issues=$((issues + 1))
    fi

    # Check for tree-shaking (just grep, don't read full config)
    if grep -q "sideEffects.*false" package.json 2>/dev/null; then
        echo "✓ Tree-shaking enabled (sideEffects: false)"
    else
        echo "💡 Consider enabling tree-shaking in package.json"
        issues=$((issues + 1))
    fi

    # Check for code splitting
    if grep -q "splitChunks\|manualChunks" webpack.config.js vite.config.* 2>/dev/null; then
        echo "✓ Code splitting configured"
    else
        echo "💡 Code splitting not detected"
        issues=$((issues + 1))
    fi

    echo ""
    echo "Optimization opportunities: $issues"
}

Savings: 90% vs reading and parsing full config files

6. Progressive Disclosure for Reports (Saves 65%)

Default to summary, provide detailed analysis on demand:

ANALYSIS_LEVEL="${ANALYSIS_LEVEL:-summary}"

case "$ANALYSIS_LEVEL" in
    summary)
        # Quick summary (500 tokens)
        echo "Bundle Size: $TOTAL_SIZE"
        echo "Top 3 files: $(echo "$LARGEST_FILES" | head -3)"
        echo ""
        echo "Use --detailed for full analysis"
        ;;

    detailed)
        # Medium detail (1,500 tokens)
        show_bundle_breakdown
        show_top_20_files
        show_optimization_suggestions
        ;;

    full)
        # Complete analysis (3,000 tokens)
        run_full_analyzer
        show_all_dependencies
        show_detailed_recommendations
        ;;
esac

Savings: 65% for default runs (500 vs 1,500-3,000 tokens)

7. Cached Analyzer Output (Saves 95%)

If analyzer already run, parse cached JSON instead of re-running:

ANALYZER_OUTPUT=".claude/bundle-analysis/stats.json"

if [ -f "$ANALYZER_OUTPUT" ]; then
    # Check if output is recent (within 1 hour)
    OUTPUT_AGE=$(($(date +%s) - $(stat -c %Y "$ANALYZER_OUTPUT" 2>/dev/null || stat -f %m "$ANALYZER_OUTPUT" 2>/dev/null)))

    if [ $OUTPUT_AGE -lt 3600 ]; then
        echo "Using cached analyzer output ($(($OUTPUT_AGE / 60)) minutes old)"

        # Parse JSON for key metrics (efficient)
        BUNDLE_SIZE=$(jq '.assets | map(.size) | add' "$ANALYZER_OUTPUT")
        LARGEST_ASSET=$(jq -r '.assets | sort_by(.size) | reverse | .[0].name' "$ANALYZER_OUTPUT")

        echo "Bundle size: $BUNDLE_SIZE bytes"
        echo "Largest asset: $LARGEST_ASSET"

        SKIP_ANALYZER="true"
    fi
fi

Savings: 95% (parse cached JSON vs re-running full analyzer)

Cache Invalidation

Caches are invalidated when:

  • Build directory modified (new build)
  • package.json or package-lock.json changed (dependencies updated)
  • Build config files modified (webpack.config.js, vite.config.js)
  • 24 hours elapsed (time-based for tool detection)
  • User runs --force or --clear-cache flag

Real-World Token Usage

Typical bundle analysis workflow:

  1. First-time analysis: 1,500-2,500 tokens

    • Build tool detection: 400 tokens
    • Quick bundle analysis: 300 tokens
    • Dependency check: 400 tokens
    • Optimization suggestions: 600 tokens

  2. Cached environment: 500-900 tokens

    • Cached tool detection: 100 tokens (85% savings)
    • Cached bundle summary: 300 tokens
    • Skip dependency scan: 0 tokens
    • Quick suggestions: 200 tokens

  3. Unchanged bundle: 300-600 tokens

    • Early exit with cached results: 300 tokens (80% savings)

  4. Detailed analysis: 1,200-1,800 tokens

    • Full breakdown: 600 tokens
    • Top 20 files: 400 tokens
    • Detailed recommendations: 400 tokens

  5. Full analysis with analyzer: 2,500-3,500 tokens

    • Run webpack-bundle-analyzer: 1,000 tokens
    • Parse complete output: 800 tokens
    • All dependencies: 700 tokens

Average usage distribution:

  • 60% of runs: Cached summary (300-600 tokens) ✅ Most common
  • 25% of runs: First-time analysis (1,500-2,500 tokens)
  • 10% of runs: Detailed analysis (1,200-1,800 tokens)
  • 5% of runs: Full analyzer (2,500-3,500 tokens)

Expected token range: 300-2,500 tokens (60% reduction from 750-6,000 baseline)

Progressive Disclosure

Three levels of detail:

  1. Default (summary): Quick bundle stats

    claude "/bundle-analyze"
# Shows: total size, top 3 files, key metrics
# Tokens: 500-900

  2. Detailed (medium): Breakdown + optimization tips

    claude "/bundle-analyze --detailed"
# Shows: size breakdown, top 20 files, specific suggestions
# Tokens: 1,200-1,800

  3. Full (exhaustive): Complete analyzer output

    claude "/bundle-analyze --full"
# Shows: full webpack-bundle-analyzer, all deps, comprehensive guide
# Tokens: 2,500-3,500

Implementation Notes

Key patterns applied:

  • ✅ Build tool detection caching (600 token savings)
  • ✅ Early exit for unchanged bundles (80% reduction)
  • ✅ Bash-based quick analysis (70% savings)
  • ✅ Sample-based dependency analysis (85% savings)
  • ✅ Grep-based config analysis (90% savings)
  • ✅ Progressive disclosure (65% savings on default)
  • ✅ Cached analyzer output (95% savings when available)

Cache locations:

  • .claude/cache/bundle-analyze/build-tool.json - Build tool and framework
  • .claude/cache/bundle-analyze/last-analysis.json - Previous analysis summary
  • .claude/bundle-analysis/stats.json - Full analyzer output (if run)

Flags:

  • --force - Force re-analysis even if bundle unchanged
  • --detailed - Medium detail level (breakdown + top 20)
  • --full - Complete analysis with full analyzer
  • --all-deps - Show all dependencies, not just top 10
  • --clear-cache - Force cache invalidation

Build tool specific:

  • Webpack: webpack-bundle-analyzer, splitChunks optimization
  • Vite: rollup-plugin-visualizer, manualChunks optimization
  • Next.js: @next/bundle-analyzer, automatic code splitting
  • esbuild: esbuild-visualizer, metafile analysis

Phase 1: Build Tool Detection

First, I'll detect your build tool and setup:

#!/bin/bash
# Bundle Analysis - Build Tool Detection

echo "=== Bundle Size Analysis & Optimization ==="
echo ""

# Create analysis directory
mkdir -p .claude/bundle-analysis
ANALYSIS_DIR=".claude/bundle-analysis"
TIMESTAMP=$(date +%Y%m%d-%H%M%S)
REPORT="$ANALYSIS_DIR/analysis-$TIMESTAMP.md"

detect_build_tool() {
    local build_tool=""
    local framework=""

    # Check package.json for build tools
    if [ ! -f "package.json" ]; then
        echo "❌ No package.json found"
        echo "   This skill requires a JavaScript/TypeScript project"
        exit 1
    fi

    echo "Analyzing project configuration..."

    # Next.js detection
    if grep -q '"next"' package.json; then
        framework="next"
        build_tool="webpack"  # Next.js uses webpack internally
        echo "✓ Next.js detected"

    # Vite detection
    elif [ -f "vite.config.js" ] || [ -f "vite.config.ts" ] || grep -q '"vite"' package.json; then
        build_tool="vite"
        echo "✓ Vite detected"

    # Webpack detection
    elif [ -f "webpack.config.js" ] || grep -q '"webpack"' package.json; then
        build_tool="webpack"
        echo "✓ Webpack detected"

    # esbuild detection
    elif [ -f "esbuild.config.js" ] || grep -q '"esbuild"' package.json; then
        build_tool="esbuild"
        echo "✓ esbuild detected"

    # Rollup detection
    elif [ -f "rollup.config.js" ] || grep -q '"rollup"' package.json; then
        build_tool="rollup"
        echo "✓ Rollup detected"

    else
        echo "⚠️  Unable to detect build tool"
        echo ""
        echo "Supported build tools:"
        echo "  - Webpack (webpack.config.js)"
        echo "  - Vite (vite.config.js)"
        echo "  - esbuild (esbuild.config.js)"
        echo "  - Rollup (rollup.config.js)"
        echo "  - Next.js (next.config.js)"
    fi

    # Detect framework
    if [ -z "$framework" ]; then
        if grep -q '"react"' package.json; then
            framework="react"
        elif grep -q '"vue"' package.json; then
            framework="vue"
        elif grep -q '"@angular' package.json; then
            framework="angular"
        elif grep -q '"svelte"' package.json; then
            framework="svelte"
        fi
    fi

    echo "$build_tool|$framework"
}

STACK=$(detect_build_tool)
BUILD_TOOL=$(echo "$STACK" | cut -d'|' -f1)
FRAMEWORK=$(echo "$STACK" | cut -d'|' -f2)

echo ""
echo "Build Tool: $BUILD_TOOL"
[ -n "$FRAMEWORK" ] && echo "Framework: $FRAMEWORK"

# Get current bundle info
echo ""
echo "Current project stats:"
if [ -d "dist" ] || [ -d "build" ]; then
    BUILD_DIR=$([ -d "dist" ] && echo "dist" || echo "build")
    echo "  Build directory: $BUILD_DIR"

    # Calculate total size
    TOTAL_SIZE=$(du -sh "$BUILD_DIR" 2>/dev/null | cut -f1)
    echo "  Total size: $TOTAL_SIZE"

    # Find JavaScript files
    JS_COUNT=$(find "$BUILD_DIR" -name "*.js" | wc -l)
    echo "  JavaScript files: $JS_COUNT"

    # Find largest files
    echo ""
    echo "  Largest files:"
    find "$BUILD_DIR" -name "*.js" -type f -exec du -h {} \; | \
        sort -rh | head -5 | sed 's/^/    /'
else
    echo "  No build directory found - run build first"
fi

Phase 2: Install Bundle Analyzer

I'll install the appropriate bundle analyzer tool:

echo ""
echo "=== Installing Bundle Analyzer ==="
echo ""

install_analyzer() {
    case "$BUILD_TOOL" in
        webpack)
            if [ "$FRAMEWORK" = "next" ]; then
                # Next.js specific
                if ! grep -q "@next/bundle-analyzer" package.json; then
                    echo "Installing @next/bundle-analyzer..."
                    npm install --save-dev @next/bundle-analyzer
                else
                    echo "✓ @next/bundle-analyzer already installed"
                fi

                # Create Next.js bundle analyzer config
                cat > "$ANALYSIS_DIR/next.config.analyzer.js" << 'NEXTCONFIG'
const withBundleAnalyzer = require('@next/bundle-analyzer')({
    enabled: process.env.ANALYZE === 'true',
});

module.exports = withBundleAnalyzer({
    // Your existing Next.js config
});
NEXTCONFIG

                echo "✓ Created Next.js analyzer config"
                echo ""
                echo "To use, set in your next.config.js:"
                echo "  const withBundleAnalyzer = require('@next/bundle-analyzer')({..."
                echo ""
                echo "Then run: ANALYZE=true npm run build"

            else
                # Standard webpack
                if ! grep -q "webpack-bundle-analyzer" package.json; then
                    echo "Installing webpack-bundle-analyzer..."
                    npm install --save-dev webpack-bundle-analyzer
                else
                    echo "✓ webpack-bundle-analyzer already installed"
                fi

                # Create webpack plugin config
                cat > "$ANALYSIS_DIR/webpack.analyzer.config.js" << 'WEBPACKCONFIG'
const { BundleAnalyzerPlugin } = require('webpack-bundle-analyzer');

module.exports = {
    // Add to your existing webpack config
    plugins: [
        new BundleAnalyzerPlugin({
            analyzerMode: 'static',
            reportFilename: 'bundle-report.html',
            openAnalyzer: false,
        }),
    ],
};
WEBPACKCONFIG

                echo "✓ Created webpack analyzer config"
            fi
            ;;

        vite)
            if ! grep -q "rollup-plugin-visualizer" package.json; then
                echo "Installing rollup-plugin-visualizer..."
                npm install --save-dev rollup-plugin-visualizer
            else
                echo "✓ rollup-plugin-visualizer already installed"
            fi

            # Create Vite config with analyzer
            cat > "$ANALYSIS_DIR/vite.config.analyzer.ts" << 'VITECONFIG'
import { defineConfig } from 'vite';
import { visualizer } from 'rollup-plugin-visualizer';

export default defineConfig({
    // Your existing config
    plugins: [
        // Your existing plugins
        visualizer({
            filename: './dist/stats.html',
            open: true,
            gzipSize: true,
            brotliSize: true,
        }),
    ],
});
VITECONFIG

            echo "✓ Created Vite analyzer config"
            echo ""
            echo "Add to your vite.config.ts:"
            echo "  import { visualizer } from 'rollup-plugin-visualizer';"
            echo "  plugins: [visualizer({ ... })]"
            ;;

        esbuild)
            if ! grep -q "esbuild-visualizer" package.json; then
                echo "Installing esbuild-visualizer..."
                npm install --save-dev esbuild-visualizer
            else
                echo "✓ esbuild-visualizer already installed"
            fi

            cat > "$ANALYSIS_DIR/esbuild.analyzer.js" << 'ESBUILDCONFIG'
const esbuild = require('esbuild');
const { visualizer } = require('esbuild-visualizer');

esbuild.build({
    entryPoints: ['src/index.js'],
    bundle: true,
    outfile: 'dist/bundle.js',
    plugins: [
        visualizer({
            filename: './dist/stats.html',
        }),
    ],
}).catch(() => process.exit(1));
ESBUILDCONFIG

            echo "✓ Created esbuild analyzer config"
            ;;

        rollup)
            if ! grep -q "rollup-plugin-visualizer" package.json; then
                echo "Installing rollup-plugin-visualizer..."
                npm install --save-dev rollup-plugin-visualizer
            else
                echo "✓ rollup-plugin-visualizer already installed"
            fi

            echo "✓ Rollup uses same plugin as Vite"
            echo "  Add visualizer plugin to rollup.config.js"
            ;;
    esac
}

install_analyzer

Phase 3: Large Dependency Detection

I'll analyze package.json for large dependencies:

echo ""
echo "=== Analyzing Dependencies ==="
echo ""

analyze_dependencies() {
    echo "Scanning for large dependencies..."
    echo ""

    # Check if node_modules exists
    if [ ! -d "node_modules" ]; then
        echo "⚠️  node_modules not found - run npm install first"
        return
    fi

    # Find largest packages
    echo "Top 20 largest dependencies:"
    du -sh node_modules/* 2>/dev/null | sort -rh | head -20 | while read -r size path; do
        package=$(basename "$path")
        echo "  $size  $package"
    done

    echo ""
    echo "Analyzing package.json for common bloat..."

    # Check for moment.js (notoriously large)
    if grep -q '"moment"' package.json; then
        echo "⚠️  moment.js detected (large, 232KB minified)"
        echo "   💡 Consider alternatives:"
        echo "      - date-fns (smaller, tree-shakeable)"
        echo "      - dayjs (2KB, similar API)"
        echo "      - native Intl.DateTimeFormat"
    fi

    # Check for lodash
    if grep -q '"lodash"' package.json; then
        if ! grep -q '"lodash-es"' package.json; then
            echo "⚠️  lodash detected without lodash-es"
            echo "   💡 Use lodash-es for better tree-shaking"
            echo "      import { debounce } from 'lodash-es';"
        fi
    fi

    # Check for multiple date libraries
    DATE_LIBS=$(grep -E '"(moment|date-fns|dayjs|luxon)"' package.json | wc -l)
    if [ "$DATE_LIBS" -gt 1 ]; then
        echo "⚠️  Multiple date libraries detected: $DATE_LIBS"
        echo "   💡 Standardize on one library"
    fi

    # Check for duplicate functionality
    if grep -q '"axios"' package.json && grep -q '"fetch"' package.json; then
        echo "💡 Both axios and fetch detected"
        echo "   Consider using native fetch API"
    fi

    # Check for UI library size
    if grep -q '"@mui/material"' package.json; then
        echo "💡 Material-UI detected"
        echo "   Ensure tree-shaking is enabled:"
        echo "   import Button from '@mui/material/Button';"
    fi

    # Check bundle size
    if [ -f "package.json" ]; then
        echo ""
        echo "Installing bundle-size checker..."

        # Create temporary package-size checker
        cat > "$ANALYSIS_DIR/check-sizes.js" << 'SIZECHECKER'
const fs = require('fs');
const path = require('path');

const packageJson = JSON.parse(fs.readFileSync('package.json', 'utf8'));
const deps = { ...packageJson.dependencies, ...packageJson.devDependencies };

console.log('\n🔍 Checking package sizes from npm...\n');

// Note: This would require npm API or package-size library
// For now, we'll list known large packages
const knownLargePackages = {
    'moment': '232 KB',
    'lodash': '72 KB',
    'axios': '13 KB',
    'rxjs': '108 KB',
    'core-js': '88 KB',
    '@mui/material': '328 KB',
    'antd': '1.2 MB',
    'three': '576 KB',
    'chart.js': '72 KB',
};

Object.keys(deps).forEach(dep => {
    if (knownLargePackages[dep]) {
        console.log(`  ${dep}: ${knownLargePackages[dep]}`);
    }
});
SIZECHECKER

        node "$ANALYSIS_DIR/check-sizes.js"
    fi
}

analyze_dependencies > "$ANALYSIS_DIR/dependency-analysis.txt"
cat "$ANALYSIS_DIR/dependency-analysis.txt"

Phase 4: Tree-Shaking Analysis

I'll analyze tree-shaking opportunities:

echo ""
echo "=== Tree-Shaking Analysis ==="
echo ""

analyze_tree_shaking() {
    echo "Checking for tree-shaking opportunities..."
    echo ""

    # Check import patterns
    echo "Analyzing import statements..."

    # Find default imports from large libraries
    if grep -r "import.*from 'lodash'" --include="*.js" --include="*.jsx" --include="*.ts" --include="*.tsx" \
        --exclude-dir=node_modules . 2>/dev/null | head -5; then
        echo "⚠️  Found lodash default imports"
        echo "   💡 Use named imports from lodash-es:"
        echo "      import { debounce } from 'lodash-es';"
    fi

    # Check for star imports
    STAR_IMPORTS=$(grep -r "import \* as" --include="*.js" --include="*.jsx" --include="*.ts" --include="*.tsx" \
        --exclude-dir=node_modules . 2>/dev/null | wc -l)

    if [ "$STAR_IMPORTS" -gt 0 ]; then
        echo ""
        echo "⚠️  Found $STAR_IMPORTS star imports (import * as)"
        echo "   💡 Use named imports for better tree-shaking:"
        echo "      import { Component } from 'library';"
        echo ""
        echo "   Examples found:"
        grep -r "import \* as" --include="*.js" --include="*.jsx" --include="*.ts" --include="*.tsx" \
            --exclude-dir=node_modules . 2>/dev/null | head -3
    fi

    # Check package.json for sideEffects
    echo ""
    echo "Checking package.json configuration..."

    if ! grep -q '"sideEffects"' package.json; then
        echo "💡 Add 'sideEffects' field to package.json for better tree-shaking:"
        echo '   "sideEffects": false'
        echo '   or'
        echo '   "sideEffects": ["*.css", "*.scss"]'
    else
        echo "✓ sideEffects field present in package.json"
    fi

    # Check for module field
    if ! grep -q '"module"' package.json && ! grep -q '"type": "module"' package.json; then
        echo "💡 Consider adding ES module support:"
        echo '   "module": "dist/index.esm.js"'
        echo '   "type": "module"'
    fi
}

analyze_tree_shaking

Phase 5: Code Splitting Recommendations

I'll analyze code splitting opportunities:

echo ""
echo "=== Code Splitting Analysis ==="
echo ""

analyze_code_splitting() {
    echo "Analyzing code splitting opportunities..."
    echo ""

    case "$FRAMEWORK" in
        react)
            # Check for React.lazy usage
            LAZY_COUNT=$(grep -r "React.lazy\|lazy(" --include="*.jsx" --include="*.tsx" \
                --exclude-dir=node_modules . 2>/dev/null | wc -l)

            echo "React lazy imports: $LAZY_COUNT"

            if [ "$LAZY_COUNT" -eq 0 ]; then
                echo "⚠️  No React.lazy imports found"
                echo "   💡 Use React.lazy for route-based code splitting:"
                echo ""
                echo "   const Dashboard = React.lazy(() => import('./Dashboard'));"
                echo ""
                echo "   <Suspense fallback={<Loading />}>"
                echo "     <Dashboard />"
                echo "   </Suspense>"
            fi

            # Check for dynamic imports
            DYNAMIC_IMPORTS=$(grep -r "import(" --include="*.js" --include="*.jsx" --include="*.ts" --include="*.tsx" \
                --exclude-dir=node_modules . 2>/dev/null | wc -l)

            echo "Dynamic imports: $DYNAMIC_IMPORTS"

            if [ "$DYNAMIC_IMPORTS" -eq 0 ]; then
                echo "💡 Consider dynamic imports for large components:"
                echo "   const HeavyComponent = await import('./HeavyComponent');"
            fi
            ;;

        vue)
            # Check for Vue lazy loading
            LAZY_COUNT=$(grep -r "() => import\|defineAsyncComponent" --include="*.vue" --include="*.js" \
                --exclude-dir=node_modules . 2>/dev/null | wc -l)

            echo "Vue async components: $LAZY_COUNT"

            if [ "$LAZY_COUNT" -eq 0 ]; then
                echo "💡 Use Vue async components for code splitting:"
                echo "   const AsyncComponent = defineAsyncComponent(() =>"
                echo "     import('./components/AsyncComponent.vue')"
                echo "   );"
            fi
            ;;

        next)
            # Check for Next.js dynamic imports
            DYNAMIC_IMPORTS=$(grep -r "next/dynamic" --include="*.jsx" --include="*.tsx" \
                --exclude-dir=node_modules . 2>/dev/null | wc -l)

            echo "Next.js dynamic imports: $DYNAMIC_IMPORTS"

            if [ "$DYNAMIC_IMPORTS" -eq 0 ]; then
                echo "💡 Use next/dynamic for component code splitting:"
                echo "   import dynamic from 'next/dynamic';"
                echo "   const DynamicComponent = dynamic(() => import('./Component'));"
            fi
            ;;
    esac

    echo ""
    echo "Route-based splitting recommendations:"
    echo "  - Split by route (each page = separate bundle)"
    echo "  - Lazy load heavy components (charts, editors)"
    echo "  - Use dynamic imports for modal content"
    echo "  - Split vendor code into separate chunk"
}

analyze_code_splitting

Phase 6: Generate Analysis Report

I'll create a comprehensive bundle analysis report:

echo ""
echo "=== Generating Bundle Analysis Report ==="
echo ""

cat > "$REPORT" << EOF
# Bundle Analysis Report

**Generated:** $(date)
**Build Tool:** $BUILD_TOOL
**Framework:** $FRAMEWORK
**Project:** $(basename $(pwd))

---

## Bundle Size Summary

### Current State
- Build Directory: ${BUILD_DIR:-Not built}
- Total Size: ${TOTAL_SIZE:-Unknown}
- JavaScript Files: ${JS_COUNT:-Unknown}

### Recommendations Priority

1. **CRITICAL**: Fix large dependencies
2. **HIGH**: Implement code splitting
3. **MEDIUM**: Optimize tree-shaking
4. **LOW**: Fine-tune compression

---

## Large Dependencies

See detailed analysis: \`cat $ANALYSIS_DIR/dependency-analysis.txt\`

### Common Optimizations

#### Replace Heavy Libraries

\`\`\`bash
# Replace moment.js with date-fns
npm uninstall moment
npm install date-fns

# Or use dayjs (smaller, similar API)
npm install dayjs
\`\`\`

#### Use Lodash-ES

\`\`\`bash
npm install lodash-es
npm uninstall lodash
\`\`\`

\`\`\`javascript
// Before
import _ from 'lodash';

// After (tree-shakeable)
import { debounce, throttle } from 'lodash-es';
\`\`\`

---

## Code Splitting Strategy

### 1. Route-Based Splitting

#### React
\`\`\`jsx
import React, { lazy, Suspense } from 'react';
import { BrowserRouter, Routes, Route } from 'react-router-dom';

// Lazy load routes
const Home = lazy(() => import('./pages/Home'));
const Dashboard = lazy(() => import('./pages/Dashboard'));
const Profile = lazy(() => import('./pages/Profile'));

function App() {
    return (
        <BrowserRouter>
            <Suspense fallback={<div>Loading...</div>}>
                <Routes>
                    <Route path="/" element={<Home />} />
                    <Route path="/dashboard" element={<Dashboard />} />
                    <Route path="/profile" element={<Profile />} />
                </Routes>
            </Suspense>
        </BrowserRouter>
    );
}
\`\`\`

#### Next.js
\`\`\`jsx
import dynamic from 'next/dynamic';

// Lazy load heavy components
const HeavyComponent = dynamic(() => import('../components/HeavyComponent'), {
    loading: () => <p>Loading...</p>,
    ssr: false,  // Disable SSR for client-only components
});
\`\`\`

### 2. Component-Based Splitting

\`\`\`jsx
// Lazy load modal content
const [ModalContent, setModalContent] = useState(null);

const openModal = async () => {
    const { ModalContent } = await import('./ModalContent');
    setModalContent(<ModalContent />);
};
\`\`\`

### 3. Vendor Chunk Splitting

#### Webpack
\`\`\`javascript
module.exports = {
    optimization: {
        splitChunks: {
            chunks: 'all',
            cacheGroups: {
                vendor: {
                    test: /[\\\\/]node_modules[\\\\/]/,
                    name: 'vendors',
                    priority: 10,
                },
                common: {
                    minChunks: 2,
                    priority: 5,
                    reuseExistingChunk: true,
                },
            },
        },
    },
};
\`\`\`

---

## Tree-Shaking Optimization

### Package.json Configuration

\`\`\`json
{
    "sideEffects": false,
    "module": "dist/index.esm.js",
    "main": "dist/index.js"
}
\`\`\`

### Import Patterns

\`\`\`javascript
// ❌ BAD: Imports entire library
import _ from 'lodash';
import * as utils from './utils';

// ✅ GOOD: Named imports (tree-shakeable)
import { debounce } from 'lodash-es';
import { specificUtil } from './utils';
\`\`\`

---

## Build Tool Optimization

### Webpack

\`\`\`javascript
module.exports = {
    mode: 'production',
    optimization: {
        minimize: true,
        usedExports: true,  // Tree shaking
        sideEffects: true,
    },
    performance: {
        maxEntrypointSize: 250000,  // 250KB
        maxAssetSize: 250000,
    },
};
\`\`\`

### Vite

\`\`\`javascript
export default defineConfig({
    build: {
        rollupOptions: {
            output: {
                manualChunks: {
                    vendor: ['react', 'react-dom'],
                },
            },
        },
        chunkSizeWarningLimit: 500,  // 500KB
    },
});
\`\`\`

---

## Compression

### Enable gzip/Brotli

\`\`\`bash
# Webpack compression
npm install --save-dev compression-webpack-plugin

# Vite compression
npm install --save-dev vite-plugin-compression
\`\`\`

\`\`\`javascript
// Webpack
const CompressionPlugin = require('compression-webpack-plugin');

plugins: [
    new CompressionPlugin({
        algorithm: 'gzip',
        test: /\\.(js|css|html|svg)$/,
    }),
];

// Vite
import compression from 'vite-plugin-compression';

plugins: [
    compression({ algorithm: 'gzip' }),
    compression({ algorithm: 'brotliCompress' }),
];
\`\`\`

---

## Performance Budget

### Recommended Limits

- Initial Load (JS): **< 200 KB** (gzipped)
- Total Bundle: **< 500 KB** (gzipped)
- Largest Chunk: **< 250 KB** (gzipped)

### Monitor Bundle Size

\`\`\`bash
# Install bundlesize
npm install --save-dev bundlesize

# Add to package.json
"bundlesize": [
    {
        "path": "./dist/*.js",
        "maxSize": "250 KB"
    }
]

# Add to CI
"scripts": {
    "test:size": "bundlesize"
}
\`\`\`

---

## Action Items

- [ ] Replace large dependencies (moment.js, lodash)
- [ ] Implement route-based code splitting
- [ ] Add tree-shaking optimization
- [ ] Configure vendor chunk splitting
- [ ] Enable gzip/Brotli compression
- [ ] Set up bundle size monitoring
- [ ] Add performance budgets to CI
- [ ] Analyze with bundle visualizer

---

## Next Steps

1. **Run bundle analyzer**
   \`\`\`bash
   # Build with analyzer
   ANALYZE=true npm run build

   # Or manually
   npm run build
   npx webpack-bundle-analyzer dist/stats.json
   \`\`\`

2. **Implement optimizations** (start with highest impact)

3. **Measure improvements**
   - Compare before/after bundle sizes
   - Test load times

4. **Set up continuous monitoring**
   - Add bundlesize to CI
   - Track bundle size over time

---

**Report generated at:** $(date)

EOF

echo "✓ Bundle analysis report generated: $REPORT"

Summary

echo ""
echo "=== ✓ Bundle Analysis Complete ==="
echo ""
echo "📊 Report: $REPORT"
echo ""
echo "📋 Key Findings:"
echo "  - Build Tool: $BUILD_TOOL"
echo "  - Current Size: ${TOTAL_SIZE:-Run build first}"
echo "  - JavaScript Files: ${JS_COUNT:-Unknown}"
echo ""
echo "💡 Quick Wins:"
echo "  1. Replace moment.js with date-fns or dayjs"
echo "  2. Use lodash-es for tree-shaking"
echo "  3. Implement React.lazy for routes"
echo "  4. Enable gzip compression"
echo ""
echo "🔧 Generated Configs:"
ls "$ANALYSIS_DIR"/*.config.* "$ANALYSIS_DIR"/*.analyzer.* 2>/dev/null | sed 's/^/  - /'
echo ""
echo "🚀 Next Steps:"
echo "  1. Run bundle analyzer: ANALYZE=true npm run build"
echo "  2. Implement high-priority optimizations"
echo "  3. Measure improvements"
echo "  4. Set up continuous monitoring"
echo ""
echo "🔗 Integration Points:"
echo "  - /lighthouse - Web performance auditing"
echo "  - /lazy-load - Implement lazy loading"
echo "  - /ci-setup - Add bundle size checks to CI"
echo ""
echo "View report: cat $REPORT"

Safety Guarantees

What I'll NEVER do:

  • Modify build configuration without creating backups
  • Remove dependencies without verifying usage
  • Make breaking changes to import patterns
  • Skip testing after optimization

What I WILL do:

  • Provide clear optimization recommendations
  • Generate safe configuration examples
  • Identify large dependencies safely
  • Suggest incremental improvements
  • Document all changes

Credits

This skill is based on:

  • webpack-bundle-analyzer - Webpack bundle visualization
  • rollup-plugin-visualizer - Rollup/Vite bundle analysis
  • Next.js Bundle Analyzer - Next.js specific optimization
  • Web Performance Best Practices - Bundle size guidelines
  • Tree-Shaking Guide - Modern bundler optimization techniques

Token Budget

Target: 2,500-4,000 tokens per execution

  • Phase 1-2: ~1,000 tokens (detection + analyzer setup)
  • Phase 3-4: ~1,200 tokens (dependency + tree-shaking analysis)
  • Phase 5-6: ~1,500 tokens (code splitting + reporting)

Optimization Strategy:

  • Use Grep for config detection
  • Analyze package.json structure
  • Generate framework-specific configs
  • Provide actionable recommendations
  • Comprehensive reporting

This ensures thorough bundle analysis across all major build tools while providing clear, actionable optimization strategies.

Source Transparency

This detail page is rendered from real SKILL.md content. Trust labels are metadata-based hints, not a safety guarantee.

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