Socket.IO: "UnhandledPromiseRejectionWarning: Error: Callbacks are not supported when broadcasting" - node.js

Question

im trying to create a login system with Node.js, Socket.IO and MongoDB.
At one point i have to get a certain cookie of the client.
So i "send" an event to the client which should return the cookie so i can work with that data within the same function.
My code is as follows:
Server:
async function checklogin(user) {
user = user;
console.log("user:", user);
await User.find({username:user}).then(function(docs) {
servercookieid = docs[0].cookieid;
servercookiedate = docs[0].cookiedate;
});
io.emit('getCookie', function(responseData) {
console.log(responseData)
}).catch(error)
}
Client:
socket.on('getCookie', function(callback) {
console.log('getting cookie...');
var Cookie = document.cookie;
callback(Cookie)
});
I really dont know why i get this error, because as you can see i am not even broadcasting, sooo...
/shrug
If you need more information, please dont hesitate to ask.

Answer 1

The error message says:
Socket.IO: “UnhandledPromiseRejectionWarning: Error: Callbacks are not
supported when broadcasting”
But in fact when you do io.emit you're broadcasting.
Currently you're broadcasting when you do the command:
io.emit('getCookie', function(responseData) {
console.log(responseData)
}).catch(error)
But for broadcasting you just need set a parameter, it's not a function.
Just fix your code to fix the error.
Changing to:
io.emit('getCookie', responseData);//must set the cookie
by the code you provided responseData is not defined. But by the name it should be a cookie.