Analysis of the causes of hot update failure

Analysis of Hot Module Replacement (HMR) Failure Causes

Hot Module Replacement (HMR) is a core feature of Vite.js, but it may fail during actual development. Here are common causes and solutions:

Circular Dependency

Circular dependencies can break HMR boundaries. For example:

// a.js
import { b } from './b'
export const a = 'A'

// b.js
import { a } from './a'
export const b = 'B'

When modifying a.js, Vite may fail to trigger updates correctly. Solutions:

1. Refactor code to eliminate circular dependencies
2. Use dynamic imports to break the cycle

// Modified b.js
export const b = 'B'
export function getA() {
  return import('./a').then(m => m.a)
}

State Management Library Integration Issues

Libraries like Redux/Vuex require special handling for HMR:

// store.js
const store = createStore(reducer)

if (import.meta.hot) {
  import.meta.hot.accept('./reducer', newModule => {
    store.replaceReducer(newModule.default)
  })
}

Common issues include:

• Incorrect use of import.meta.hot.accept
• Incomplete state replacement logic
• Failure to clean up side effects

CSS Processing Exceptions

Configuration issues with preprocessors like PostCSS/Less/Sass may cause style updates to fail:

// vite.config.js
export default {
  css: {
    postcss: {
      plugins: [require('autoprefixer')]
    },
    modules: {
      // Must configure localsConvention for correct class name mapping
      localsConvention: 'camelCase'
    }
  }
}

Typical symptoms:

• No page changes after modifying styles
• Styles update but class name mapping is incorrect
• Preprocessor cache not cleared

Improper Custom HMR Boundary Handling

Errors often occur when manually defining HMR boundaries:

// Correct approach
if (import.meta.hot) {
  import.meta.hot.accept(['./dep1', './dep2'], ([newDep1, newDep2]) => {
    // Handle updates
  })
}

// Error example 1: Missing callback function
import.meta.hot.accept('./module')

// Error example 2: Not checking if hot exists
import.meta.hot.accept(/*...*/)

Browser Cache Interference

Improper dev server configuration may cause browsers to cache old resources:

// vite.config.js
export default {
  server: {
    headers: {
      'Cache-Control': 'no-store'
    }
  }
}

Also check:

• Whether browser has strong caching enabled
• If Service Worker is intercepting requests
• Whether incorrect URL strategies are used

Plugin Conflicts

Certain Vite plugins may interfere with HMR:

// Problematic plugin configuration
import legacy from '@vitejs/plugin-legacy'

export default {
  plugins: [
    legacy({
      targets: ['defaults']
    }),
    // May conflict with other plugins
  ]
}

Troubleshooting steps:

1. Disable plugins one by one for testing
2. Check plugin documentation for HMR compatibility notes
3. Update plugins to the latest version

Filesystem Event Loss

File watching may fail in WSL or virtual machine environments:

# Solution: Increase polling interval
export default {
  server: {
    watch: {
      usePolling: true,
      interval: 1000
    }
  }
}

Other related factors:

• File permission issues
• inotify watch limits
• Antivirus software interference

Dynamic Import Path Issues

Dynamically imported modules may fail to trigger HMR correctly:

// Problem code
const module = await import(`./dir/${name}.js`)

// Solution 1: Use glob imports
const modules = import.meta.glob('./dir/*.js')

// Solution 2: Explicitly declare dependencies
if (import.meta.hot) {
  import.meta.hot.accept(['./dir/a.js', './dir/b.js'], /*...*/)
}

Third-party Library Compatibility Issues

Some libraries require special configuration:

// Correct configuration for React
import { defineConfig } from 'vite'
import react from '@vitejs/plugin-react'

export default defineConfig({
  plugins: [react({
    // Must enable fast refresh
    fastRefresh: true
  })]
})

Common problematic libraries:

• Older jQuery plugins
• Unadapted Web Components
• Global state management libraries

Improper Environment Variable Usage

Environment variable changes may cause module re-execution instead of hot updates:

// Wrong usage: Directly using environment variables
const apiUrl = import.meta.env.VITE_API_URL

// Improved solution: Manage through configuration center
let config = {
  apiUrl: import.meta.env.VITE_API_URL
}

if (import.meta.hot) {
  import.meta.hot.accept('./config', newConfig => {
    config = newConfig
  })
}

Custom File Type Handling

Non-standard file extensions require explicit configuration:

// vite.config.js
export default {
  assetsInclude: ['**/*.glsl'],
  plugins: [{
    name: 'custom-hmr',
    handleHotUpdate({ file, server }) {
      if (file.endsWith('.glsl')) {
        server.ws.send({ type: 'full-reload' })
      }
    }
  }]
}

Browser Extension Interference

Some dev tool extensions may:

• Inject their own HMR client
• Modify DOM causing Vite to lose control
• Intercept network requests

Testing methods:

1. Use incognito mode
2. Disable extensions one by one
3. Check console errors

Network Configuration Issues

Proxy settings may cause WebSocket connection failures:

export default {
  server: {
    proxy: {
      '/api': 'http://localhost:3000',
      // Must explicitly configure WebSocket
      '/socket.io': {
        target: 'ws://localhost:3000',
        ws: true
      }
    },
    // Ensure host is configured correctly
    host: '0.0.0.0'
  }
}