ErrorEvent Trouble Resolution

The bug was that the argument to an onerror handler is merely an Event, not an ErrorEvent. Doing a web search shows that there has historically been confusion about which of the two the argument should be, but the MDN documentation is clear.

Outdated Explanation (see above)

This is a "minimal" test case that shows that in certain circumstances, an ErrorEvent::message invocation will cause WASM running in a web browser to fail in an unrecoverable way. Specifically, the ErrorEvent passed to the onerror handler of a WebSocket will not be able to call message().

To reproduce

Install trunk and then have trunk run the program:

$ cargo install trunk
$ trunk serve --open

Now open up your JavaScript console and you should see something like:

09:38:42.243 WebSocket connection to 'wss://example.com/not-available' failed: 
09:38:42.243 Uncaught
TypeError: Cannot read properties of undefined (reading 'length')
    at passStringToWasm0 (error-event-8348614ec5312283.js:142:19)
    at imports.wbg.__wbg_message_730094b985f3ba2e (error-event-8348614ec5312283.js:485:22)
    at error_event-77a5375a3ee8a4dc.wasm.web_sys::features::gen_ErrorEvent::ErrorEvent::message::h53ae803a5f72d5d2 (error-event-8348614ec5312283_bg.wasm:0xb3c8c)
    at error_event-77a5375a3ee8a4dc.wasm.<error_event::App as yew::functional::FunctionProvider>::run::app::{{closure}}::hea26a0e2e6a812a6 (error-event-8348614ec5312283_bg.wasm:0xbb828)
    at error_event-77a5375a3ee8a4dc.wasm.<dyn core::ops::function::Fn<(:8080/A,)>+Output = R as wasm_bindgen::closure::WasmClosure>::describe::invoke::h826fadf1d4a4f6fd (http://127.0.0.1:8080/error-event-8348614ec5312283_bg.wasm)
    at __wbg_adapter_20 (error-event-8348614ec5312283.js:208:10)
    at WebSocket.real (error-event-8348614ec5312283.js:194:20)

The first complaint "WebSocket connection ... failed" is just a warning and, although annoying to some, doesn't prevent the WASM from continuing. The second error is the problem.

Trunk and Yew

I realize that by requiring trunk and yew as dependencies that this isn't really minimal. However, I am not particularly familiar with JavaScript ecosystem particulars. My company's (closed-source) software uses yew with webpack on the front-end and actix-web on the back-end. So, this same behavior happens with webpack and trunk, which makes me guess that this is problem is at the web-sys level.

Cliff Matthews