我尝试在Express服务器中实现套接字，代码如下所示：应用程序类：

app: Application;
server: http.Server | https.Server;
sockets: SocketIo;

constructor() {
   this.app = express();
   this.app.use(cors());
   this.server = http.createServer(this.app);
   this.iniciarSockets();
   this.server.listen(3000, () => .....)
}

private async iniciarSockets() {
 this.sockets = new SocketIo(this.server);
}

我的SocketIo类看起来像这样：

import http from 'http';
import https from 'https';
import { Server, Socket } from 'socket.io';
export class SocketIo {
  io: Server;

  constructor(server: http.Server | https.Server) {
      this.io = require("socket.io")(server);

       this.io.on("connection", (socket: Socket) => {
          console.log("New connection");
          socket.emit("test event", "Here is some data");
        
      })
}
}

但是当我尝试使用服务从Angular访问它时，我在控制台中得到以下三个错误：404 socket.io/?EIO=4&transport=polling&t=OXzMsOL Not Found（Not Found）404 Not Found（Not Found）
访问XMLHttpRequest在'http：//localhost：3000/socket.io/？EIO=4&transport=polling&t=OXzMsOR' from origin ' http：//localhost：4200 ' has been blocked by CORS policy：请求的资源上不存在“Access-Control-Allow-Origin”标头。
GET http：//localhost：3000/socket.io/?EIO=4&transport=polling&t=OXzMsOR net：：ERR_FAILED 200（OK）
我的Angular服务看起来像这样，我在Youtube上看了一段视频：

export class WebSocketService {

  socket: any;
  readonly url: string = "ws://localhost:3000";

  constructor() {
    this.socket = io(this.url);
   }

  listen(eventName: string) {
    return new Observable((subscriber) => {
      this.socket.on(eventName, (data) => {
        subscriber.next(data);
      })
    })
  }

  emit(eventName: string, data: any) {
    this.socket.emit(eventName, data);
  }
}