How to get response from socket.on before calling socket.emit - node.js

Question

I am using node.js for creating an application that is maintaing the repository for the courses and its respective lectures and slides. And the retreival of courses of student (from mysql Db) is based on student name, the retreival of lectures is based on course name and soo on. The student name is stored on server and i must get it before calling server for getting course list.
Here is my code with more explanation:
var StdName;
$(document).ready(function () {
//connect to server
connectBind();
var socket = $("#click").data();
/**********Query database For student name!!!**********/
try {
socket.emit('askStdName');
}
catch (err) {
alert(err.message);
}
/********Query database For Courses!!!************/
try {
socket.emit('view-contents', StdName);
}
catch (err) {
alert(err.message);
}
});
//connecting to server
function connectBind() {
// connect to server on this port.
var socket = io.connect('http://localhost:3000');
$("#click").data(socket);
/**********GETTING NAME OF STUDENT*********/ //I WANT TO GET STUDENT NAME BEFORE THE QUERY FOR COURSES GET CALLED
try {
socket.on('get-Studentname', function (data) {
StdName = data;
alert("StdName: " + StdName);
});
}
catch (err) {
alert(err.Message);
}
And here is the server side script:
var express = require('express'); //load express
var http = require('http'); // then http
var socketIO = require('socket.io'); // then socket
var mysql = require('mysql');
var nodemailer = require("nodemailer");
var client = mysql.createConnection({
host: 'localhost',
user: 'root',
password: '',
database: 'smartboard_db'
});
client.connect();
var app = express(); // create application
var server = http.createServer(app); //create server
var io = socketIO.listen(server); // start listening to server.
io.set('log level', 2);
// setup routing for static files.
app.use(express.static(__dirname + '/public'));
//start server
server.listen(3000, function(){
console.log('Server running...');
});
// First page
app.get('/', function(request, response) {
response.sendfile(__dirname + '/student-home.html');
});
io.set('log level', 1);
io.sockets.on('connection', function (socket) {
var sucess;
console.log("client connected");
/************SENDING THE NAME TO CLIENT*************/
socket.on('askStdName', function () {
console.log('sending student name to client');
socket.emit('get-Studentname', stdName);
});
/***********CHANNEL FOR GETTING COURSE LIST************/
socket.on('view-contents', function (stdName) {
//console.log("this is what I get from client for courses: " + stdName);
var DATABASE = 'smartboard_db';
client.query('USE ' + DATABASE);
/*****QUEURY FOR COURSES *****************/
client.query('SELECT courses FROM student_info WHERE name = "' + stdName + '"', function (err, results) {
if (err) {
throw err;
}
else {
console.log(JSON.stringify({ courses: results }));
socket.emit('courses', JSON.stringify({ courses: results }));
}
});
});
});
Can ny one help please?

Answer 1

If the get-Studentname event should always be followed by getting the courses:
// request student name
socket.emit('askStdName');
// wait for the student name to be returned, followed by requesting the courses
socket.on('get-Studentname', function (StdName) {
socket.emit('view-contents', StdName);
});
Alternatively, you can pass a function with the request for the student name, which the server can call to send back the response (instead of having the server emit a response). This does require a different setup on your server though:
// client code
socket.emit('askStdName', function(StdName) {
socket.emit('view-contents', StdName);
});
// server code should look like this:
socket.on('askStdName', function(done) {
// get student name (depends on your setup)
...
// call the function to return the value
done(StdName);
});