Showing job progress using SignalR in WebForms client

question
1

I am executing a long-running process using Hangfire. I want to let the
client know the progress (% complete) using Microsoft.AspNet.SignalR.
So far I am able to execute the job, but I cannot understand how to add
the SignalR part. This is what I have so far.

// BEGIN Startup.cs
public partial class Startup {
        public void Configuration(IAppBuilder app) {
            ConfigureAuth(app);
            app.MapSignalR();
            GlobalConfiguration.Configuration.UseSqlServerStorage(
                "DefaultConnection",
                new SqlServerStorageOptions { QueuePollInterval = TimeSpan.FromSeconds(1) });

            app.UseHangfireDashboard();
            app.UseHangfireServer();
        }
    }
// END Startup.cs

// BEGIN TestForm.cs
public partial class TestForm : System.Web.UI.Page
{
    protected void cmdOK_Click(object sender, EventArgs e)
    {
        string id = 
            BackgroundJob.Enqueue(() => LongRunner.LongRunningMethod());
        
    }
}
// END TestForm.cs

// BEGIN LongRunner.cs
class LongRunner
{
    static int _percent = 0;
    // declare public method to be executed by Hangfire

    public static void LongRunningMethod()
    {
        int oldPercent = _percent;
        for (int i = 0; i < 600; i++)
        {
            // if % complete changes, notify client
            _percent = i / 6;
            if (oldPercent != _percent)
            {
                oldPercent = _percent;
                // I believe that this is where SignalR comes in
            }
            System.Threading.Thread.Sleep(100);
        }
    }
}
// END LongRunner.cs

This works. When I go to the dashboard, I see that the job executed and
it took about 1 minute as expected.

I want to update the TestForm web page when there is something to
report, i.e., when the percentage complete increases. I understand that
I have to define a hub:

// BEGIN LongRunnerHub.cs
class LongRunnerHub : Hub
{
    // Don't really know what this does
    await Groups.Add(Context.ConnectionId, "LongRunnerGroup");
    
    // or what should be here.
}
// END LongRunnerHub.cs

I must also change my long running method:

// BEGIN LongRunner.cs
class LongRunner
{
    static int _percent = 0;
    
    // declare public method to be executed by Hangfire
    public static void LongRunningMethod()
    {
        var hubContext = GlobalHost.ConnectionManager
        .GetHubContext<LongRunnerHub>();

        hubContext.Clients.Group("LongRunnerGroup")
        . // Don't know what goes here
        
        int oldPercent = _percent;
        for (int i = 0; i < 600; i++)
        {
            // if % complete changes, notify client
            _percent = i / 6;
            if (oldPercent != _percent)
            {
                oldPercent = _percent;
                // Notify client, but how?
            }
            System.Threading.Thread.Sleep(100);
        }
    }
}
// END LongRunner.cs

Please help me fill in the blanks. All the SignalR examples show HTML pages + Javascript. Is it that I must write Javascript or will ASP.NET WebForms take care of that for me?