问3000端口已经在使用。Nodejs，套接字，IO

EN

const port = process.env.port || 3000;

app.listen((port), () => console.log(`listening to port ${port}`));

const io = require("socket.io")(port) //Here's the problem. 

listening to port 3000
events.js:292
      throw er; // Unhandled 'error' event
      ^

Error: listen EADDRINUSE: address already in use :::3000

Emitted 'error' event on Server instance at:
    at emitErrorNT (net.js:1345:8)
    at processTicksAndRejections (internal/process/task_queues.js:80:21) {
  code: 'EADDRINUSE',
  errno: -4091,
  syscall: 'listen',
  address: '::',
  port: 3000
}
[nodemon] app crashed - waiting for file changes before starting...