Island JS chunks not being cached (Cache-Control: no-cache) when using @fresh/plugin-vite

[andreluizsgf]

Hi! I'm running into an issue with island caching behavior that seems different of the expected behavior.

From my understanding, Fresh should cache island JS bundles aggressively (immutable, long max-age) when served from paths like:

/_fresh/js/{BUILD_ID}/chunk-XXXX.js

However, that's not what I'm observing in my app.

What I'm seeing:

• Every page refresh triggers new HTTP requests for all islands
• The number of server requests remains the same between first and subsequent visits
• Each island request includes:
  • Cache-Control: no-cache
  • A new X-Deno-Trace-Id on every refresh
  • 
• This suggests that nothing is being served from browser cache

In traces, each island appears as a separate request on every reload.

Expected behavior:

• First visit → island chunks fetched and cached
• Subsequent visits → served from browser cache (no network requests)
• After deploy → only changed chunks fetched

Environment:

@fresh/plugin-vite@1.0.8
vite@7.2.7
Using Vite builder (not legacy)

Important detail:

From discussion, it was mentioned that Fresh only applies caching to assets served from:

/_fresh/js/{BUILD_ID}/...

or assets suffixed with:

?__frsh_c=BUILD_ID

In my case, the island assets seem to be served from a different path, assets/fresh-island..., which might explain why caching headers are not applied.

Below there is my vite.config.ts

vite.config.ts

import { defineConfig } from 'vite';
import { fresh } from '@fresh/plugin-vite';
import tailwindcss from '@tailwindcss/vite';
import { initializeRoutes } from '@utils/router.ts';

export default defineConfig({
  plugins: [
    fresh({
      islandSpecifiers: ['@ui/components-loader', '@hooks', '@stores', '@lib/islands/global-config.tsx'],
    }),
    tailwindcss(),
    // Plugin to stub out all core-js imports
    {
      name: 'initialize-routes',
      enforce: 'pre',
      buildStart() {
        initializeRoutes('painel');
      },
    },
    {
      name: 'stub-core-js',
      enforce: 'pre',
      resolveId(id) {
        // Only stub actual core-js module imports, not anything that includes 'core' in the name
        if (id.startsWith('core-js/modules/') || id === 'core-js' || id.startsWith('core-js/internals/')) {
          return '\0virtual:empty-module';
        }
      },
      load(id) {
        if (id === '\0virtual:empty-module') {
          return 'export default {};';
        }
      },
    },
  ],
  resolve: {
    alias: {
      // Rollup (via @fresh/plugin-vite) doesn't apply CJS default interop for these helpers.
      // canvg imports the CJS helpers with `import x from ...`, so point to the ESM variants.
      '@babel/runtime/helpers/defineProperty': '@babel/runtime/helpers/esm/defineProperty',
      '@babel/runtime/helpers/asyncToGenerator': '@babel/runtime/helpers/esm/asyncToGenerator',
      // Replace ALL @babel/runtime-corejs3 imports with @babel/runtime (no core-js)
      '@babel/runtime-corejs3/helpers/defineProperty': '@babel/runtime/helpers/esm/defineProperty',
      '@babel/runtime-corejs3/helpers/asyncToGenerator': '@babel/runtime/helpers/esm/asyncToGenerator',
      '@babel/runtime-corejs3/helpers/esm/defineProperty': '@babel/runtime/helpers/esm/defineProperty',
      '@babel/runtime-corejs3/helpers/esm/asyncToGenerator': '@babel/runtime/helpers/esm/asyncToGenerator',
      // Redirect any core-js module imports to empty module
      'core-js/modules/es.regexp.to-string.js': 'data:text/javascript,export default {}',
      'core-js/modules/es.array.iterator.js': 'data:text/javascript,export default {}',
      'core-js/modules/es.object.to-string.js': 'data:text/javascript,export default {}',
      'core-js/modules/es.promise.js': 'data:text/javascript,export default {}',
      'core-js/modules/es.string.iterator.js': 'data:text/javascript,export default {}',
      'node:module': 'node:module',
    },
  },
  optimizeDeps: {
    esbuildOptions: {
      treeShaking: true,
    },
  },
  ssr: {
    external: [
      'jspdf',
      'quill',
      'quill-magic-url',
      'dompurify',
      'html2canvas',
      'canvg',
      '@babel/runtime-corejs3',
    ],
  },
  server: {
    port: 8000,
  },
});
</details> ```