can someone explain from where in my console comes undefined value? - node.js

Question

if i go to localhost:8080/?referal=referalID in my console i got referall id and also one line of undefined value, how can i remove that undefined line?
var http = require('http');
var url = require('url');
http.createServer(function(req,res){
res.writeHead(200, {'Content-Type':'text/html'});
var adr = req.url;
var q = url.parse(adr, true);
var qdata = q.query;
res.end(console.log(qdata.referal));
}).listen(8080);
my question is what i need to change here?

Answer 1

I'm not sure what you're trying to do there, however this should be the correct syntax:
var http = require('http');
var url = require('url');
http.createServer(function(req,res) {
var adr;
var q;
var qdata;
req.on('data', function() {
// Data handler
}).on('end', function() {
res.writeHead(200, {'Content-Type':'text/html'});
adr = req.url;
q = url.parse(adr, true);
qdata = q.query;
console.log(qdata);
res.end(qdata.referal);
});
}).listen(8080);

Answer 2

You cannot send a console.log call in the response.
You should separate the two:
console.log(qdata.referal); // This will print in the console, server side
res.end(qdata.referal) // This will be echoed back to the client, in the browser

Answer 3

The reason you see undefined is because your browser is also looking for favicon.ico so your function gets hit twice. If you do:
var http = require('http');
var url = require('url');
http.createServer(function(req,res){
res.writeHead(200, {'Content-Type':'text/html'});
var adr = req.url;
console.log(adr);
var q = url.parse(adr, true);
var qdata = q.query;
res.end(qdata.referal);
}).listen(8080);
you will get:
/?referal=referalID
/favicon.ico
The result of url.parse('/favicon.ico', true); is undefined.
Also as others mentioned res.end(console.log(qdata.referal)); won't return anything to the browser/client because console.log() doesn't return anything.

Answer 4

The undefined line you probably talking about is the one returns to the client, that's because console log doesn't return anything
as you can see in the source code here
Override console logging to return the arguments
['log', 'warn', 'error'].forEach(function(method) {
var oldMethod = console[method].bind(console);
console[method] = function() {
oldMethod.apply(console, arguments);
return arguments;
};
});
Although this might save couple opcodes and pushing another object into the stack, you should use this with caution or memorize a pray that will help you with future-related-bugs.
Next time, please attach log or screenshot
#over-programming