doc suggestion: do not use express app.listen() with socket.io

I ran into this in the process of adding socket.io to an existing express(4) app because i didn’t switch the code from app.listen() to server.listen().

The symptom is refusal by the server to serve the client library or connect any sockets.

According to http://expressjs.com/4x/api.html#app.listen , “This method is identical to node’s http.Server.listen()” - but in reality it creates a new http server leaving the one with socket.io non-operational.

Hopefully this issue will help others to avoid the same trap.

[TifPun]

+1

Did a bit more research and found a way (more details here) to stick with app.listen():

var io = require("socket.io").listen(server);
app.set("port", (process.env.PORT || 3000));
var server = app.listen(app.get("port"), function(){
  console.log("Server started: http://localhost:" + app.get("port") + "/");
})

which seems to work the same as:

var io = require("socket.io")(server);
var server = require('http').Server(app);
server.listen((process.env.PORT || 3000), function(){
  console.log("Server started: http://localhost:" + app.get("port") + "/");
});

[darrachequesne]

This is indeed a common trap… A note was added here: https://socket.io/docs/v3/server-initialization/#With-Express