Socket.io 2.1.0请求出现404错误，寻求非降级解决方案

Let's jump straight to fixing your issue—no need to roll back versions. The 404 error you're seeing stems from two easy-to-fix gaps in your setup.

Why the Error Happens #

Your request is hitting http://localhost/socket.io/ instead of the correct http://localhost:3000/socket.io/ because:

1. Your server isn't actually running on port 3000—you forgot to start the HTTP listener, so Socket.io's endpoint doesn't exist at that port.
2. The client connection code has a redundant call that can lead to unintended default behavior.

Step 1: Fix the Server Code #

This is the most critical change. Add the missing port listener to your server.js to launch your Express and Socket.io services on 3000:

var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);

app.get('/', function(req, res){
  res.sendFile(__dirname + '/index.html');
});

io.on('connection', function(socket){
  socket.on('chat message', function(msg){
    io.emit('chat message', msg);
  });
});

// Add this line to start listening on port 3000
http.listen(3000, function(){
  console.log('listening on *:3000');
});

Step 2: Simplify the Client Connection #

Socket.io 2.x doesn't require combining io() and connect()—simplify your client code to explicitly target the correct server URL, eliminating any ambiguity:

<script src="http://localhost:3000/socket.io/socket.io.js"></script>
<script src="https://code.jquery.com/jquery-1.11.1.js"></script>
<script>
  $(function () {
    // Directly specify the server URL for clear, reliable connection
    var socket = io('http://localhost:3000');
    $('form').submit(function(){
      socket.emit('chat message', $('#m').val());
      $('#m').val('');
      return false;
    });
    socket.on('chat message', function(msg){
      $('#messages').append($('<li>').text(msg));
    });
  });
</script>

Final Quick Checks #

• Access your app via http://localhost:3000 (don't open index.html directly with the file:// protocol—this causes cross-origin issues).
• Restart your server after making changes, then refresh the client page.

This should resolve the 404 error completely while keeping you on Socket.io 2.1.0.

内容的提问来源于stack exchange，提问作者User