🐞 Bug report: Ironically, WASM workers do not work in the production build.

[GianfrancoBazzani]

Describe the bug

I am using Vite + React for a tiny UI. I used WASM with web workers to enable multi-threading. The app is working on the dev server, but in the bundled production build, I am having problems.

I used rustwasm/wasm-bindgen and wasm-pack to generate JavaScript bindings for a Wasm binary, and then I built a TypeScript wrapper around it to achieve worker behavior. I think that since, in the JavaScript artifact generated by Wasm, the .wasm file is not explicitly imported (see), it doesn't get included in the bundle (though I'm not entirely sure). I tried different configurations without getting it to work. :(

I tried following plugins without getting it to work:

• @zebing/vite-plugin-wasm-pack
• vite-plugin-wasm

Reproduction

https://github.com/GianfrancoBazzani/uni-v4-hook-address-miner/tree/main/ui

Steps to reproduce

With minimal reproducible example codebase

1. clone GianfrancoBazzani/vite-react-wasm-webwokers-example
2. cd vite-react-wasm-webwokers-example
3. nvm use to ensure node v20.18.0
4. yarn to install deps
5. yarn build-wasm-worker to build the wasm worker and the js bidings
6. yarn build to build the production page
7. yarn dev to start the dev server at http://localhost:5173/
8. yarn preview to start production preview at http://localhost:4173/
9. Press Greet from worker in both instances, you will see that in dev server the wasm worker is returning the string "Hello from the web worker!" while in prod is not :(.

With problematic codebase GianfrancoBazzani/uni-v4-hook-address-miner

1. clone GianfrancoBazzani/uni-v4-hook-address-miner
2. cd uni-v4-hook-address-miner/ui
3. yarn
4. yarn build
5. yarn preview
6. If you run the miner the woker never starts.

System Info

System:
    OS: Linux 6.12 Arch Linux
    CPU: (20) x64 13th Gen Intel(R) Core(TM) i7-1370P
    Memory: 51.78 GB / 62.39 GB
    Container: Yes
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.18.0 - ~/.nvm/versions/node/v20.18.0/bin/node
    Yarn: 1.22.22 - ~/.nvm/versions/node/v20.18.0/bin/yarn
    npm: 10.8.2 - ~/.nvm/versions/node/v20.18.0/bin/npm
    pnpm: 9.15.3 - ~/.nvm/versions/node/v20.18.0/bin/pnpm
  Browsers:
    Brave Browser: 131.1.73.97
  npmPackages:
    @vitejs/plugin-react-swc: ^3.5.0 => 3.7.2 
    vite: ^6.0.1 => 6.0.7

Used Package Manager

yarn

Logs

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[GianfrancoBazzani]

Proceeding to close since I found the problem:

• problem explanation
• workarround introduced in 91560a4