How to use C# WebAssemly from JavaScript without Blazor web components

Question

To compile C# into WebAssemly and interop with JS it's required to use Blazor WebAssembly ASP.NET framework, which is designed for SPA and contains lot of overhead in case you just want to use a C# library from JS.

What is the minimum setup to just compile a DLL to WebAssembly and use it from JavaScript?

Answer 1

Create a new empty C# project with the following configuration (via .csproj):

<Project Sdk="Microsoft.NET.Sdk.BlazorWebAssembly">

    <PropertyGroup>
        <TargetFramework>net6.0</TargetFramework>
        <LangVersion>10</LangVersion>
    </PropertyGroup>

    <ItemGroup>
        <PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly" Version="6.0.0" />
        <PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly.DevServer" Version="6.0.0" PrivateAssets="all" />
    </ItemGroup>

</Project>

Initialize Blazor JS runtime and specify the bindings:

namespace WasmTest;

public class Program
{
    private static IJSRuntime js;

    private static async Task Main (string[] args)
    {
        var builder = WebAssemblyHostBuilder.CreateDefault(args);
        var host = builder.Build();
        js = host.Services.GetRequiredService<IJSRuntime>();
        await host.RunAsync();
    }

    [JSInvokable]
    public static async Task<string> BuildMessage (string name)
    {
        var time = await GetTimeViaJS();
        return $"Hello {name}! Current time is {time}.";
    }

    public static async Task<DateTime> GetTimeViaJS ()
    {
        return await js.InvokeAsync<DateTime>("getTime");
    }
}

Publish with dotnet publish and use the C# library from JS:

<script src="_framework/blazor.webassembly.js" autostart="false"></script>

<script>
    window.getTime = () => {
        return new Date().toJSON();
    };
    window.onload = async function () {
        await Blazor.start();
        const msg = await DotNet.invokeMethodAsync("WasmTest", "BuildMessage", "John");
        console.log(msg);
    };
</script>

Here is an example template solution on GitHub: https://github.com/Elringus/WasmTest