How does Rspack's Hot Module Replacement (HMR) work?

Hot Module Replacement (HMR) is one of Rspack's core features, offering significant performance improvements compared to Webpack's HMR. Here's a detailed explanation of Rspack's HMR:

HMR Basic Principles

Hot Module Replacement allows modules to be updated during development when they change, without refreshing the entire page. This maintains application state and improves the development experience.

Advantages of Rspack HMR

1. Extremely Fast Update Speed:

   • Rspack's HMR update speed can reach millisecond levels
   • Compared to Webpack, update speed is improved by 10-50x
   • Advantages are more obvious in large projects

2. Intelligent Module Updates:

   • Only recompiles and transfers changed modules
   • Intelligently identifies module dependencies, minimizing update scope
   • Supports fine-grained module replacement

3. State Preservation:

   • Maintains application state during updates
   • Avoids user experience interruptions caused by page refreshes
   • Preserves form inputs, scroll positions, and other states

4. Error Recovery:

   • Automatically rolls back when updates fail
   • Provides friendly error messages
   • Supports manual triggering of reloads

HMR Configuration

Rspack's HMR configuration is very simple and enabled by default in development mode:

javascript
// rspack.config.js
module.exports = {
  mode: 'development',
  devServer: {
    hot: true, // Enable HMR
    // Other devServer configurations
  }
}

HMR API

Rspack provides an HMR API compatible with Webpack:

javascript
// Using HMR API in modules
if (module.hot) {
  module.hot.accept('./dependency.js', function() {
    // Execute when dependency module is updated
    console.log('Dependency updated');
  });
  
  module.hot.dispose(function() {
    // Execute cleanup before module is replaced
    console.log('Module will be replaced');
  });
}

Framework Integration

Rspack's HMR integration with mainstream frontend frameworks:

1. React:

   • Supports React Fast Refresh
   • Updates components while maintaining component state
   • Automatically handles functional and class components

2. Vue:

   • Supports Vue's HMR
   • Maintains component state and instances
   • Supports hot updates for Single File Components (SFC)

3. Other Frameworks:

   • Supported through framework-specific HMR plugins
   • Most frameworks have ready-to-use integration solutions

Performance Optimization

Rspack's HMR performance optimizations include:

1. Incremental Compilation:

   • Only compiles changed modules
   • Uses caching to avoid redundant compilation
   • Processes multiple modules in parallel

2. Intelligent Updates:

   • Analyzes module dependency graph to minimize update scope
   • Only transfers necessary code
   • Uses WebSocket for efficient update transmission

3. Memory Optimization:

   • Efficient memory management
   • Avoids memory leaks
   • Supports long development sessions

Best Practices

1. Reasonable Use of HMR API:

   • Only use HMR API when necessary
   • Properly handle module cleanup logic
   • Avoid time-consuming operations in HMR callbacks

2. Configuration Optimization:

   • Adjust HMR configuration based on project scale
   • Reasonably set timeout values
   • Enable necessary HMR plugins

3. Error Handling:

   • Monitor HMR error events
   • Provide friendly error messages
   • Implement automatic recovery mechanisms

Rspack's HMR feature provides developers with an ultimate development experience, significantly improving development efficiency, especially in large projects.