在Blazor WebAssembly项目中，可以使用JSRuntime来模拟IHostApplicationLifetime的功能。下面是一个示例：

首先，在Program.cs文件中添加以下代码，以模拟IHostApplicationLifetime的功能：

using Microsoft.JSInterop;
using System;
using System.Threading.Tasks;

public class MyHostApplicationLifetime
{
    private readonly IJSRuntime _jsRuntime;
    private bool _applicationStopping;

    public event Action ApplicationStopping;

    public MyHostApplicationLifetime(IJSRuntime jsRuntime)
    {
        _jsRuntime = jsRuntime;
    }

    public void StopApplication()
    {
        if (!_applicationStopping)
        {
            _applicationStopping = true;
            OnApplicationStopping();
        }
    }

    protected virtual void OnApplicationStopping()
    {
        ApplicationStopping?.Invoke(new ApplicationStoppingEventArgs());
    }

    public class ApplicationStoppingEventArgs : EventArgs
    {
    }
}

public static class MyHostApplicationLifetimeExtensions
{
    public static async Task WaitForApplicationStoppingAsync(this MyHostApplicationLifetime hostApplicationLifetime)
    {
        var tcs = new TaskCompletionSource