express javascript node.js npm sockets

In nodeJs on method is unresolved in webstorm

I am learning in node and i have installed the module using-

npm install --save

here is my code

var app = require('express')();
var http = require('http').Server(app);
var io = require('')(http);
app.get('/', function(req, res){
io.on('connection', function(socket){
console.log('a user connected');
http.listen(3000, function(){
console.log('listening on *:3000');

enter image description here

but webstorm is saying that ‘on’ is unresolved .. please help