How does Rspack's Tree Shaking work?

Tree Shaking is an important optimization technology for modern frontend build tools. Rspack implements efficient Tree Shaking functionality that can effectively remove unused code and reduce bundle size. Here's a detailed explanation of Rspack's Tree Shaking:

Basic Principles of Tree Shaking

The core idea of Tree Shaking is to identify and remove unused code by statically analyzing module import and export relationships. Just like shaking a tree where dead leaves fall off, unused code is "shaken" off.

Rspack Tree Shaking Mechanism

1. Static Analysis:

   • Analyze ES Module import/export syntax
   • Build module dependency graph
   • Identify whether exported content is used

2. Mark Unused Code:

   • Mark unused exports
   • Mark unused functions and variables
   • Analyze side effects

3. Code Removal:

   • Remove unused code during code generation
   • Optimize final bundle size
   • Maintain code correctness

Role of ES Module

Tree Shaking only works with ES Module because:

• ES Module import/export is static and can be analyzed at compile time
• CommonJS require is dynamic and cannot be statically analyzed
• ES Module structure is clearer, making dependency analysis easier

javascript
// ES Module - Supports Tree Shaking
export const add = (a, b) => a + b;
export const subtract = (a, b) => a - b;

// Only import add, subtract will be Tree Shaken
import { add } from './math';

// CommonJS - Does not support Tree Shaking
module.exports = {
  add: (a, b) => a + b,
  subtract: (a, b) => a - b
};

Side Effects Handling

Side effects refer to modules that produce certain effects when imported, such as modifying global variables or executing certain operations. Rspack provides multiple ways to handle side effects:

1. package.json Configuration:

   json
   {
     "name": "my-package",
     "sideEffects": false
   }

   • false: Indicates the module has no side effects and can be safely Tree Shaken
   • true: Indicates the module has side effects and cannot be Tree Shaken
   • Array: Specifies files with side effects

2. Specify in Configuration:

   javascript
   module.exports = {
     optimization: {
       usedExports: true,
       sideEffects: true
     }
   }

Optimization Configuration

Rspack provides multiple optimization options to enhance Tree Shaking effects:

javascript
module.exports = {
  mode: 'production',
  optimization: {
    usedExports: true, // Mark unused exports
    sideEffects: true, // Handle side effects
    minimize: true, // Enable code minification
    concatenateModules: true // Module concatenation
  }
}

Practical Application Examples

1. Utility Library Optimization:

   javascript
   // utils.js
   export const formatDate = (date) => { /* ... */ };
   export const parseDate = (date) => { /* ... */ };
   export const validateDate = (date) => { /* ... */ };
   
   // main.js
   import { formatDate } from './utils';
   // parseDate and validateDate will be Tree Shaken

2. Component Library Optimization:

   javascript
   // components.js
   export { Button } from './Button';
   export { Input } from './Input';
   export { Modal } from './Modal';
   
   // App.js
   import { Button } from './components';
   // Input and Modal will be Tree Shaken

3. Third-party Library Optimization:

   • Use libraries that support Tree Shaking (like lodash-es)
   • Avoid importing entire libraries

   javascript
   // Not recommended
   import _ from 'lodash';
   
   // Recommended
   import { debounce } from 'lodash-es';

Considerations

1. Ensure ES Module Usage:

   • Set "type": "module" in package.json
   • Or use .mjs extension
   • Or enable ES Module support in configuration

2. Properly Handle Side Effects:

   • Carefully evaluate whether modules have side effects
   • Avoid incorrect marking that leads to code being incorrectly deleted
   • Test functionality after Tree Shaking

3. Production Environment Testing:

   • Verify Tree Shaking effects in production environment
   • Check if bundle size is reduced
   • Ensure functionality works correctly

4. Code Style:

   • Use named exports instead of default exports
   • Avoid executing side effect operations at module top level
   • Keep code modular and analyzable

Performance Optimization Recommendations

1. Analyze Build Results:

   • Use Rspack's analysis tools to see which code is removed
   • Identify modules that can be further optimized
   • Monitor Tree Shaking effects

2. Optimize Import Methods:

   • Use named imports instead of default imports
   • Avoid importing entire modules
   • Use dynamic imports for on-demand loading

3. Choose Appropriate Libraries:

   • Prioritize libraries that support Tree Shaking
   • Avoid using libraries with side effects
   • Consider using lighter alternatives

Rspack's Tree Shaking feature provides developers with powerful code optimization capabilities. Through reasonable configuration and usage, it can significantly reduce bundle size and improve application performance.