Socket constructor issue in node.js

I have following code in node.js.

const express = require("express");
var socket = require("socket.io");

class Server {

    constructor() {
        this.app = express();
        this.port = process.env.PORT || 89;
        this.host = process.env.HOST || `192.168.43.173:89`;
    }

    includeRoutes() {
    }

    appExecute() {

        var server = this.app.listen(this.port, () => {
            console.log(`Listening on http://${this.host}`);
        });     
        var io = socket(server);
    }
}
const server = new Server();
server.appExecute();

below are the dependencies exist in package.json file.

"express": "^4.17.1",
"socket.io": "^2.3.0"

I am facing an issue when the line is executed var io = socket(server);

Error Details.

Unexpected Token ...options.

Here is the screenshot.

Can you please suggest something? If you need more info, please let me know