net6.0: Runtime error: invokeJSFromDotNet creating HostBuilder

[LukeTOBrien]

Hello,

This error has ruined my entire day and as a last resort I am posting here.
My project was using net5.0 and I have recent updated to 6.0 - Are there any additional migration steps from 5 to 6?
I would also like to ask where can I find the unminified source for blazor.webassembly.js?

If you look at the bottom it say the error is on line 16 which is var builder = WebAssemblyHostBuilder.CreateDefault(args);
The stack trace also says InitializeNavigationManager - The main component is doing JS Interop inside OnAfterRenderAsync but I don't think it's getting this far.

I have absolutely no idea.
Any ideas what I can do to help solve?

The error appears at runtime in the Dev console of the browser:

(I am using Parcel for bundling, hence the filename index.abc.js)

index.6bce0794.js:1 System.AggregateException: One or more errors occurred. (n8 is not defined
ReferenceError: n8 is not defined
    at Object.Rt [as invokeJSFromDotNet] (https://localhost:7013/index.6bce0794.js:1:63608)
    at _mono_wasm_invoke_js_blazor (https://localhost:7013/_framework/dotnet.6.0.0.fkurqlj2a7.js:1:193780)
    at wasm://wasm/00945abe:wasm-function[2588]:0x8065b
    at wasm://wasm/00945abe:wasm-function[2307]:0x689a7
    at wasm://wasm/00945abe:wasm-function[7015]:0x17bac4
    at wasm://wasm/00945abe:wasm-function[6830]:0x172bc5
    at wasm://wasm/00945abe:wasm-function[3524]:0xb47cc
    at wasm://wasm/00945abe:wasm-function[675]:0x16602
    at wasm://wasm/00945abe:wasm-function[6727]:0x16f60e
    at Object.Module._mono_wasm_invoke_method [as invoke_method] (https://localhost:7013/_framework/dotnet.6.0.0.fkurqlj2a7.js:1:215575))
 ---> Microsoft.JSInterop.JSException: n8 is not defined
ReferenceError: n8 is not defined
    at Object.Rt [as invokeJSFromDotNet] (https://localhost:7013/index.6bce0794.js:1:63608)
    at _mono_wasm_invoke_js_blazor (https://localhost:7013/_framework/dotnet.6.0.0.fkurqlj2a7.js:1:193780)
    at wasm://wasm/00945abe:wasm-function[2588]:0x8065b
    at wasm://wasm/00945abe:wasm-function[2307]:0x689a7
    at wasm://wasm/00945abe:wasm-function[7015]:0x17bac4
    at wasm://wasm/00945abe:wasm-function[6830]:0x172bc5
    at wasm://wasm/00945abe:wasm-function[3524]:0xb47cc
    at wasm://wasm/00945abe:wasm-function[675]:0x16602
    at wasm://wasm/00945abe:wasm-function[6727]:0x16f60e
    at Object.Module._mono_wasm_invoke_method [as invoke_method] (https://localhost:7013/_framework/dotnet.6.0.0.fkurqlj2a7.js:1:215575)
   at Microsoft.JSInterop.WebAssembly.WebAssemblyJSRuntime.InvokeUnmarshalled[Object,Object,Object,String](String identifier, Object arg0, Object arg1, Object arg2, Int64 targetInstanceId)
   at Microsoft.JSInterop.WebAssembly.WebAssemblyJSRuntime.InvokeUnmarshalled[String](String identifier)
   at Microsoft.AspNetCore.Components.WebAssembly.Hosting.WebAssemblyHostBuilder.InitializeNavigationManager(IJSUnmarshalledRuntime jsRuntime)
   at Microsoft.AspNetCore.Components.WebAssembly.Hosting.WebAssemblyHostBuilder..ctor(IJSUnmarshalledRuntime jsRuntime, JsonSerializerOptions jsonOptions)
   at Microsoft.AspNetCore.Components.WebAssembly.Hosting.WebAssemblyHostBuilder.CreateDefault(String[] args)
   at Program.<Main>$(String[] args) in C:\App\UI\UI\Program.cs:line 16
   --- End of inner exception stack trace ---

[LukeTOBrien]

Just to add more detail.
I added a breakpoint to the JS file in DevTools, the attached screenshot shows the function.

It is using jsCallDispatcher.findJSFunction to call a method Blazor._internal.navigationManager.getUnmarshalledBaseURI.
The parameters n8 and r4 seem to be both undefined.

Hope this helps :)

[SteveSandersonMS]

I would also like to ask where can I find the unminified source for blazor.webassembly.js?

It's built from TypeScript sources at https://github.com/dotnet/aspnetcore/tree/main/src/Components/Web.JS/src.

We do support customization of the deployed application file structure as described at https://devblogs.microsoft.com/dotnet/custom-deployment-layout-for-blazor-webassembly-apps/. However I'm afraid we don't specifically test for or support using the Parcel bundler and don't have any specific insights into why using that might be breaking the JavaScript file. Sorry I can't give more info here.