vite-plugin exception thrown when doing npm run build

[rajeshg]

Which Cloudflare product(s) does this pertain to?

Vite Plugin

What versions & operating system are you using?

WSL2 windows

Please provide a link to a minimal reproduction

No response

Describe the Bug

when running npm run build, in a cloudflare workers react-router v7 project, I get the following exception:

Using Vite Environment API (experimental)
vite v6.2.6 building for production...
transforming (147) node_modules/lucide-react/dist/esm/icons/chart-bar.js11:05:57 AM [vite] (ssr) ✨ new dependencies optimized: react-router, @iconify-icon/react/dist/iconify.mjs, @iconify-icon/react, lucide-react, react, next-themes, react-dom
11:05:57 AM [vite] (ssr) ✨ optimized dependencies changed. reloading
11:05:57 AM [vite] (ssr) error while updating dependencies:
AssertionError [ERR_ASSERTION]: The WebSocket is undefined
    at Object.send (file:///home/ubuntu/sde/workspace/humsub-website-rr/node_modules/@cloudflare/vite-plugin/dist/index.js:13064:7)
    at Object.send (file:///home/ubuntu/sde/workspace/humsub-website-rr/node_modules/vite/dist/node/chunks/dep-Bid9ssRr.js:44632:23)
    at fullReload (file:///home/ubuntu/sde/workspace/humsub-website-rr/node_modules/vite/dist/node/chunks/dep-Bid9ssRr.js:52484:21)
    at runOptimizer (file:///home/ubuntu/sde/workspace/humsub-website-rr/node_modules/vite/dist/node/chunks/dep-Bid9ssRr.js:52467:11)
    at processTicksAndRejections (node:internal/process/task_queues:105:5

Here is my wrangler.json

{
	"$schema": "https://unpkg.com/wrangler@latest/config-schema.json",
	"name": "website-rr",
	"main": "./app/entry.worker.ts",
	"compatibility_date": "2025-04-07",
	"compatibility_flags": ["nodejs_compat"],
	"workers_dev": true,
	"dev": { "port": 3000 },
	"placement": { "mode": "off" },
	"observability": { "enabled": true },
	"assets": { "directory": "./build/client", "binding": "ASSETS" },
	"kv_namespaces": [{ "binding": "KV", "id": "...." }]
}

It's important to note that, the project doesn't do anything with websockets by itself.
https://github.com/cloudflare/workers-sdk/blob/d04c69f81eb40a854c219fdcad53e0387ca5f2e2/packages/vite-plugin-cloudflare/src/cloudflare-environment.ts#L47C4-L48C1

Please provide any relevant error logs

No response

[jamesopstad]

Thanks for the issue. Please could you provide a reproduction so we can investigate?

[rajeshg]

Reproduction steps:

1. git clone git@github.com:rajeshg/humsub-website-rr.git
2. cd humsub-website-rr
3. bun i -- can do this with npm as well
4. bun run build

[jamesopstad]

Thanks. The issue here is that React Router creates a separate Vite dev server to use as a child compiler when running the build. We prevent creating a Miniflare instance in this case and that is the result of the errors as it tries to connect to Miniflare when discovering new dependencies. I don't think this should have any affect on your build output but we will look into how we could improve this.

[JustFly1984]

@jamesopstad I'm getting same error

[paulogr]

@jamesopstad I'm getting the same error when enabling the experimental remote binding|

wrangler.jsonc

"d1_databases": [
		{
			"binding": "DB",
			"database_name": "...",
			"database_id": "...",
			"migrations_dir": "./server/db/migrations",
			"experimental_remote": true
		}
	]

vite.config.js

cloudflare({ experimental: { remoteBindings: true }})

error

AssertionError [ERR_ASSERTION]: The WebSocket is undefined
    at Object.send (file:///home/paulogr/Workspace/glo-app/node_modules/.pnpm/@cloudflare+vite-plugin@1.12.3_vite@7.1.4_workerd@1.20250902.0_wrangler@4.34.0/node_modules/@cloudflare/vite-plugin/dist/index.js:7510:7)
    at Object.send (file:///home/paulogr/Workspace/glo-app/node_modules/.pnpm/vite@7.1.4/node_modules/vite/dist/node/chunks/dep-C6pp_iVS.js:28872:149)
    at hmr (file:///home/paulogr/Workspace/glo-app/node_modules/.pnpm/vite@7.1.4/node_modules/vite/dist/node/chunks/dep-C6pp_iVS.js:29030:20)

Thank you

[rajeshg]

@jamesopstad vite 7.1.7 release (see release notes) makes this worse and breaks the build for me.

Here are my build logs:
vite7.1.6.log
vite7.1.7.log

vite7.1.7 changed the prune behavior and that could have caused this build error, to not be ignored anymore.

My understanding is that in vite v7.1.7, the assertion is thrown while Vite is performing a transform/SSR compile step (stack contains Vite transform pipeline: handlePrunedModules -> TransformPluginContext.transform -> compileRouteFile/getRouteModuleExports). That exception bubbles up into the transform pipeline and causes the build to abort.

[GaiusValerius]

I can confirm this issue. If I define kv_namespaces in my wrangler.jsonc i also receive the same error, regardless of what's in vite.config.ts.:

            "kv_namespaces": [
                {
                    "binding": "KV",
                    "id": "REAL_KV_ID",
                },
            ],

15:58:25 [vite] (ssr) error while updating dependencies:
AssertionError [ERR_ASSERTION]: The WebSocket is undefined
    at Object.send (file:///Users/.../node_modules/@cloudflare/vite-plugin/dist/index.js:7524:7)
    at Object.send (file:///Users/.../node_modules/vite/dist/node/chunks/dep-Bm2ujbhY.js:28558:149)
    at fullReload (file:///Users/.../node_modules/vite/dist/node/chunks/dep-Bm2ujbhY.js:34572:19)
    at runOptimizer (file:///Users/.../node_modules/vite/dist/node/chunks/dep-Bm2ujbhY.js:34557:5)
    at processTicksAndRejections (node:internal/process/task_queues:105:5)

For me, this causes also the entire build to fail.

[aaronadamsCA]

To add another wrinkle, the build behaviour is apparently nondeterministic.

When I run a matrix of many completely identical builds on GitHub Actions, the failure rate is 10-20%.

Details

You can tell a build is going to fail when it announces "new dependencies optimized, optimized dependencies changed, reloading" shortly after starting. So it seems like there's some kind of race condition involving dependency optimization.

Here's a diff of the log output:

Details

--- failure
+++ success
@@ -1,15 +1,6 @@
 Using Vite Environment API (experimental)
 vite v7.1.7 building for production...
 transforming...
-5:58:29 PM [vite] (ssr) ✨ new dependencies optimized: date-fns, clsx, react-live-chat-loader, csv-stringify/browser/esm/sync
-5:58:29 PM [vite] (ssr) ✨ optimized dependencies changed. reloading
-5:58:29 PM [vite] (ssr) error while updating dependencies:
-AssertionError [ERR_ASSERTION]: The WebSocket is undefined
-    at Object.send (file://(redacted)/node_modules/.pnpm/@cloudflare+vite-plugin@1.13.8_vite@7.1.7_@types+node@24.5.2_jiti@2.6.0_lightningcss@1._da94349eb0c6817a67d8677404748158/node_modules/@cloudflare/vite-plugin/dist/index.js:6518:7)
-    at Object.send (file://(redacted)/node_modules/.pnpm/vite@7.1.7_@types+node@24.5.2_jiti@2.6.0_lightningcss@1.30.1_terser@5.44.0_yaml@2.8.1/node_modules/vite/dist/node/chunks/dep-Bm2ujbhY.js:28558:149)
-    at fullReload (file://(redacted)/node_modules/.pnpm/vite@7.1.7_@types+node@24.5.2_jiti@2.6.0_lightningcss@1.30.1_terser@5.44.0_yaml@2.8.1/node_modules/vite/dist/node/chunks/dep-Bm2ujbhY.js:34572:19)
-    at runOptimizer (file://(redacted)/node_modules/.pnpm/vite@7.1.7_@types+node@24.5.2_jiti@2.6.0_lightningcss@1.30.1_terser@5.44.0_yaml@2.8.1/node_modules/vite/dist/node/chunks/dep-Bm2ujbhY.js:34557:5)
-    at processTicksAndRejections (node:internal/process/task_queues:105:5)
 ✓ 1477 modules transformed.
 Generated an empty chunk: "route".
 Generated an empty chunk: "route".
@@ -211,122 +202,15 @@
 build/client/assets/Menu-CMVk_ojy.js                           90.66 kB │ gzip: 31.34 kB
 build/client/assets/chunk-NISHYRIK-D45w4Fpp.js                116.89 kB │ gzip: 39.53 kB
 build/client/assets/entry.client-UW0zQkF3.js                  182.65 kB │ gzip: 58.21 kB
-✓ built in 7.50s
+✓ built in 8.12s
 vite v7.1.7 building SSR bundle for production...
 transforming...
-✓ 136 modules transformed.
-✗ Build failed in 1.18s
-[react-router:virtual-modules] Could not load virtual:react-router/server-manifest (imported by virtual:react-router/server-build): The WebSocket is undefined
-file: (redacted)/(redacted)/route.tsx
-AssertionError [ERR_ASSERTION]: The WebSocket is undefined
-    at Object.send (file://(redacted)/node_modules/.pnpm/@cloudflare+vite-plugin@1.13.8_vite@7.1.7_@types+node@24.5.2_jiti@2.6.0_lightningcss@1._da94349eb0c6817a67d8677404748158/node_modules/@cloudflare/vite-plugin/dist/index.js:6518:7)
-    at Object.send (file://(redacted)/node_modules/.pnpm/vite@7.1.7_@types+node@24.5.2_jiti@2.6.0_lightningcss@1.30.1_terser@5.44.0_yaml@2.8.1/node_modules/vite/dist/node/chunks/dep-Bm2ujbhY.js:28558:149)
-    at handlePrunedModules (file://(redacted)/node_modules/.pnpm/vite@7.1.7_@types+node@24.5.2_jiti@2.6.0_lightningcss@1.30.1_terser@5.44.0_yaml@2.8.1/node_modules/vite/dist/node/chunks/dep-Bm2ujbhY.js:28869:6)
-    at TransformPluginContext.transform (file://(redacted)/node_modules/.pnpm/vite@7.1.7_@types+node@24.5.2_jiti@2.6.0_lightningcss@1.30.1_terser@5.44.0_yaml@2.8.1/node_modules/vite/dist/node/chunks/dep-Bm2ujbhY.js:29813:24)
-    at processTicksAndRejections (node:internal/process/task_queues:105:5)
-    at EnvironmentPluginContainer.transform (file://(redacted)/node_modules/.pnpm/vite@7.1.7_@types+node@24.5.2_jiti@2.6.0_lightningcss@1.30.1_terser@5.44.0_yaml@2.8.1/node_modules/vite/dist/node/chunks/dep-Bm2ujbhY.js:30984:14)
-    at compileRouteFile ((redacted)/node_modules/.pnpm/@react-router+dev@7.9.3_@types+node@24.5.2_babel-plugin-macros@3.1.0_jiti@2.6.0_lightni_fb61a54fef89cc4cf59e11485d143219/node_modules/@react-router/dev/dist/vite.js:2628:21)
-    at getRouteModuleExports ((redacted)/node_modules/.pnpm/@react-router+dev@7.9.3_@types+node@24.5.2_babel-plugin-macros@3.1.0_jiti@2.6.0_lightni_fb61a54fef89cc4cf59e11485d143219/node_modules/@react-router/dev/dist/vite.js:2635:14)
-    at (redacted)/node_modules/.pnpm/@react-router+dev@7.9.3_@types+node@24.5.2_babel-plugin-macros@3.1.0_jiti@2.6.0_lightni_fb61a54fef89cc4cf59e11485d143219/node_modules/@react-router/dev/dist/vite.js:2599:27
-    at async Promise.all (index 2) {
-  generatedMessage: false,
-  code: 'PLUGIN_ERROR',
-  actual: undefined,
-  expected: true,
-  operator: '==',
-  diff: 'simple',
-  plugin: 'react-router:virtual-modules',
-  id: '(redacted)/(redacted)/route.tsx',
-  pluginCode: 'import { jsx, jsxs } from "react/jsx-runtime";\n' +
-    'import { useMemo } from "react";\n' +
-    (redacted)
-  hook: 'load',
-  watchFiles: [Array]
-}
-Error: Process completed with exit code 1.
+✓ 1978 modules transformed.
+rendering chunks...
+build/server/.vite/manifest.json                   0.72 kB
+build/server/wrangler.json                         1.22 kB
+build/server/assets/server-build-bZBIoZ3w.css     81.82 kB
+build/server/index.js                              0.12 kB │ map:     0.09 kB
+build/server/assets/worker-entry-BS1lluT1.js   1,021.89 kB │ map: 2,198.35 kB
+build/server/assets/server-build-BLHiPiHG.js   2,279.00 kB │ map: 4,318.53 kB
+✓ built in 9.60s