how to send request to specific client from socket.io server? - node.js

Question

I'm saving the users data in an array see the below code
server code
socket.on('add user', function(data) {
if (users.indexOf(data.id) == -1) {
users.push({
id: socket.id,
userId: data.id,
firstName: data.firstName,
lastName: data.lastName
});
}
len = users.length;
len--;
io.emit('user join', users, users[len].userId, users[len].id);
});
I'm sending request from front end to a user for that first i'm checking whether user in online or not for sending request to specific user. If user there I'm assigning user socket.id to userId variable based on that I'm sending data see the below code
server code
socket.on('addNewFriend', function(userId) {
console.log(userId);
for(var i=0;i<users.length;i++){
if(users[i].userId==userId){
var socketid=users[i].id;
console.log(socketid);
io.to(socketid).emit('addFriend',"hai");
}
}
});

Answer 1

Instead of keeping just the socket Id, keep the socket connection itself as well.
users.push({
id: socket.id,
socket: socket
userId: data.id,
firstName: data.firstName,
lastName: data.lastName
});
It would be easier, if you use a map, instead of an array to save users,
users[socket.id] = {
socket: socket
userId: data.id,
firstName: data.firstName,
lastName: data.lastName
}
Then when you want to send a message, use the socket connection,
users[socketId].socket.emit(/*args*/)
If you save sockets in an array instead, you will need to filter the user object manually and then do the same.
Edit: So the full code for the listener is as below,
socket.on('addNewFriend', function(userId) {
for(var i=0;i<users.length;i++){
if(users[i].userId == userId){
var socketId = users[i].id;
console.log(socketId);
users[socketId].socket.emit('addFriend', "hai");
}
}
});