为什么我无法从其他文件访问 express 服务器？

Question

I have set up an express server as follows (inside of server.js ):

const app = express();
.........
.....
const PORT = process.env.PORT || 5000;
const server = app.listen(PORT, () =>
  console.log(`Server started on port ${PORT}`)
);
module.exports = server;

Inside of another file socket.js :

const server = require("./server");
const socketio = require("socket.io");
const io = socketio(server);
io.on("connection", function (socket) {
  console.log("A user just joined!");

  socket.on("disconnect", () => {
    console.log("A socket just left!");
  });
});

For some reason I get an error in my console while trying to connect to the socketio on the client:

GET http://localhost:3000/socket.io/?EIO=3&transport=polling&t=N8-d7Q4 404 (Not Found)

The error does not occur if I execute everything in a single file (without exporting the server):

const PORT = process.env.PORT || 5000;
const server = app.listen(PORT, () =>
  console.log(`Server started on port ${PORT}`)
);
const socketio = require("socket.io");
const io = socketio(server);
io.on("connection", function (socket) {
  console.log("A user just joined!");

  socket.on("disconnect", () => {
    console.log("A socket just left!");
  });
});

I don't understand what's wrong. Does module.exports not work with the express server or is this is a socketio issue?

Answer 1

It appears you're not loading socket.js at all. When you had only the one file, you just did node app.js and that would work fine. But, if you do node app.js with your two files, then there's nothing to ever load socket.js at all. In fact, the way you have the two files laid out, you would have to do:

node socket.js

to initialize things. Then, socket.js does a require('./app.js') to get app.js loaded.

I was wondering if it's impossible to module.exports = server at all

Yes, you can freely export the server and you are exporting it.

---

Another way of doing things is to still have app.js be your main file that you load to start up your app and you load socket.js from there and pass it the server object so it can use it.

// app.js

const server = const server = app.listen(...);

// load socket.js and pass it our server
require('./socket.js')(server);

Then in socket.js:

// socket.js

const socketio = require("socket.io");

module.exports = function(server) {
     const io = socketio(server);
     // rest of your module code here
}