export a function inside socket connection - node.js

Question

I have created a socket server as shown below.
const express = require('express');
const app = express();
const server = require('http').createServer(app);
const io = require('socket.io')(server, {cors:{origin:'*'}})
const mongoose= require("mongoose")
const port = process.env.PORT || 4002;
server.listen(port, ()=>{
console.log(`Listening on port ${port}......`)
})
onlineUsers = [];
const addNewUser = (userId, socketId)=>{
!onlineUsers.some((user)=>user.userId === userId) &&
onlineUsers.push({userId,socketId})
}
const removeUser= (socketId) =>{
onlineUsers = onlineUsers.filter((user)=> user.socketId!==socketId)
}
const getUser = (userId)=>{
return onlineUsers.find(user=>user.userId ===userId)
}
io.on("connection", (socket=> {
console.log("User connected:", socket.id);
socket.on("disconnect",()=>{
removeUser(socket.id)
})
socket.on("newUser",(userId)=>{
addNewUser(userId, socket.id)
})
export function handleMessaging (userId,clientID,messageId )
{
const receiver = getUser(userId);
if(receiver)
{
io.to(receiver.socketId).emit("sendMessage", {data:"working properly"});
return true;
}
else return false
}
}));
I want to export the function handle messaging so that I can use it inside the API like (shown below) to see if a user is online and if yes, send a message.
But as someone new to programming, I can't figure out how to export handle messaging the proper way. I tried to use export but its telling me "Modifiers cannot appear here".
router.post('/:companyId' async (req, res) => {
const {userId,clientId,messageId} = req.body
handleMessaging (userId,clientID,messageId )
{
//do xyz
}
}