Tasks returned from JSRuntime.InvokeAsync during OnInitAsync never finishes in preview3

[kvantetore]

Describe the bug

Tasks returned from JSRuntime.InvokeAsync during second call to OnInitAsync (after prerendering) never finishes.

To Reproduce

Create a new razorcomponents project.

Add a js interop function to Index.cshtml and disable prerendering

    <script>
        window.interopDuringOnInit = function() {
            return "Hello World";
        }
    </script>

    <app></app>

    <script src="_framework/components.server.js"></script>

Call js interop during OnAsyncInit in Index.razor

<h1>@Greeting!</h1>

Welcome to your new app.

@functions {
    string Greeting;

    protected override async Task OnInitAsync()
    {
        try
        {
            Console.WriteLine("Calling browser");
            Greeting = await JSRuntime.InvokeAsync<string>("interopDuringOnInit");
            Console.WriteLine("Returned from browser");
        }
        catch (Exception ex)
        {
            Console.WriteLine("Could not invoke interop during OnInit, " + ex.ToString());
        }
    }
}

When OnInitAsync is called as part of an initial load (prerendering disabled) the task never finishes, This leaves the circuit hanging, and no further events are processed.

If this component is loaded from a IUriHelper.OnLocationChange, the above code works as expected.

[springy76]

I just switched an existing app which worked fine to the new version and got the same problem: IJSRuntime.InvokeAsync() neither returns nor throws an error on call paths from OnInitAsync().

Is there a workaround or did I do something fundamentally wrong? (which I don't believe because the same app worked since Blazor 0.3 and did every version upgrade, got converted to server side Razor Components weeks ago.)

[DNF-SaS]

Same probleme here - the await for JSRuntime.InvokeAsync() in an component's OnInitAsync() does block forever.

[Knudel]

I migrated my code to preview 3 and I also ran into this problem.
Please fix this!

[DNF-SaS]

Does anybody has news / a workaround for this issue?

[mkArtakMSFT]

@javiercn, can you please look into this? Thanks!

[KP-WhatEver]

I also got that problem. Anything worked fine before.

[kvantetore]

I have hacked around it by wrapping wrapping the router component in an if (Started), where Started is set to true after a round trip to the client. It's not exactly beautiful (and it breaks prerendering), but it unblocks the issue for me until the underlying issue is fixed.

In App.razor, delay loading the router until we have received a message from the client

@if (Started)
{
    <Router AppAssembly="typeof(Startup).Assembly" />
}
else
{
    <text>Waiting for Asp.Net Core 3.0 Preview3 Workaround...</text>
}

@functions {
    bool Started = false;

    [JSInvokable]
    public void Start()
    {
        Started = true;
        StateHasChanged();
    }

    protected override void OnInit()
    {
        _ = JSRuntime.InvokeAsync<object>("StartMe", new DotNetObjectRef(this));
    }
}

And adding window.StartMe to index.cshtml, calling back to the App component

<script>
    window.StartMe = function (dotnetHelper) {
        dotnetHelper.invokeMethodAsync('Start');
    }
</script>

[vertonghenb]

Not only does this happen on OnInitAsync but also on OnParametersSetAsync.
Using it on a ButtonClick does return.