socket.io Typescript fails to create a server, "This expression is not callable"

7
votes

I have the following code(server):

import express from "express";
import socketio from "socket.io";
import http from "http";

const app = express();
const server = http.createServer(app);
const io = socketio(server);

server.listen(process.env.port || 3000, () => {
  console.log(`App running on port ${process.env.port || 3000}`);
});

But i get an error on const io = socketio(server);, It states:

This expression is not callable. Type 'typeof import("SOME_PATH/node_modules/socket.io/dist/index")' has no call signatures

What exactly is the problem here?

package.json:

 "devDependencies": {
    "@types/express": "^4.17.11",
    "@types/node": "^14.14.27",
    "@types/socket.io": "^2.1.13",
    "nodemon": "^2.0.7",
    "ts-node": "^9.1.1"
  },
  "dependencies": {
    "express": "^4.17.1",
    "socket.io": "^3.1.1",
    "typescript": "^4.1.5"
  }
2
node.jstypescripttypessocket.io
Looks like socket.io provides its own types, but these are missing the default export factory. I'd either open up an issue or figure out how to tell TypeScript to not use the types from node_modules/socket.io but fom node_modules/@types/socket.io. – cbr
Did you check that all types are installed? Try npm i to be sure – Mike Malyi

2 Answers

15
votes

The api changed in version 3. This issue here has some discussion.

The new equivalent of your example would be

import express from "express";
import { Server } from "socket.io";
import http from "http";

const app = express();
const server = http.createServer(app);
const io = new Server(server);

server.listen(process.env.port || 3000, () => {
  console.log(`App running on port ${process.env.port || 3000}`);
});

As a side note, socket.io was rewritten in typescript, so you no longer need to have @types/socket.io.

0
votes

Not sure about that, but the problem seems to be in the way socket.io describe its own default export.

I solved this by casting it as any

    import io from 'socket.io';
    const server = (io as any)(http);