Quickstart Simple example wont run on web

[Liuzhichao99]

Hi, im new with flutter_rust_bridge. Following the quickstart from document demo
for web but can't get it to run, anyone having the same issue ?
Hello, I am currently testing the frb_example/gallery project from the master branch and encountered several issues when building for the Web target.

1. wasm-pack build --target web produces runtime errors

I built with:

wasm-pack build --release --target web --out-dir "$PROJECT_ROOT/web/pkg"

When launching the web page, the console shows:

Uncaught SyntaxError: Unexpected token 'export'
Uncaught (in promise) ReferenceError: wasm_bindgen is not defined

I checked the generated JavaScript file (rust_lib.js) and noticed that it was loaded in HTML as:

<script src="pkg/rust_lib.js"></script>

but without type="module".

This leads to the JS file being treated as classic script instead of ES module, which likely causes the export error.

rust_lib.js

2. Attempting --target no-modules produces another error

To avoid the export issue, I tried compiling with:

wasm-pack build --release --target no-modules --out-dir "$PROJECT_ROOT/web/pkg"

The page loads, but clicking UI buttons (which call Rust functions) triggers the following error:

'Worker': # could not be cloned

This prevents interaction with the Rust/WASM functions.

worker

3. The official demo also fails

The same issue occurs on the official FRB demo:

https://cjycode.com/flutter_rust_bridge/demo/

Clicking the “tap to start” button shows:

'Worker': # could not be cloned

So it seems this is not caused by my project setup.

worker

4. Environment

frb_example/gallery, master branch

wasm-pack latest version

Flutter Rust Bridge master

Tested on Chrome & Safari (same result)

5. Question

Is Web support currently broken on master?
Is there a recommended workaround or a correct configuration for using FRB with Web workers + WASM in the current version?

Any guidance would be appreciated. Thank you!

[fzyzcjy]

wasm-pack build

Hi, could you please try the commands in quickstart and see whether it works: