Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.SpaServices.Webpack;
using Microsoft.Extensions.DependencyInjection;
using VueCliMiddleware;

namespace demo11
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            app.UseStaticFiles();

            app.UseSpa(spa =>
            {
                spa.Options.SourcePath = "client";
                if (env.IsDevelopment())
                {
                    spa.UseVueCli(npmScript: "serve", port: 8080); // optional port
                }
            });
        }
    }
}