Node.js and undefined properties

Question

I'm trying to use GET variables to transfer some simple data but for some reason I'm doing it wrong.

My code is pretty simple. I use Node.js HTTP & URL libraries. When I try to run following code, I get TypeError: Cannot read property 'foo' of undefined. I really don't understand why because foo is passed in the URL and if I do console.log to q object, there's foo value.

http.createServer(function (req, res) {
   res.writeHead(200, {'Content-Type': 'text/plain'})
   var vars = url.parse(req.url,true)
   var q = vars.query
   if(q.foo) {
      res.end('yay')
   } else res.end('snif')
 }).listen(8000,"127.0.0.1")

Ivo Wetzel · Accepted Answer · 2010-11-25 13:52:31Z

4

Your problem is not that foo doesn't exist, the problem is that q itself is undefined.

Where does that come from? Well if we clean it up and add some logs...

var http = require('http');
var url = require('url');

http.createServer(function (req, res) {
    console.log(req.url);

    res.writeHead(200, {'Content-Type': 'text/plain'});
    var vars = url.parse(req.url, true);
    var q = vars.query;
    if(q && q.foo) { // this time check that q has a value (or better check that q is an object)
        res.end('yay');

    } else {
        res.end('snif');
    }
}).listen(8000,"127.0.0.1");

..we find out that the browser requests:

/bla?foo=1
/favicon.ico

There you go! Of course the favicon request has not GET params, you simply need to check that q is not undefined.

answered Nov 25, 2010 at 13:52

Ivo Wetzel

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3 Comments

Mike Over a year ago

Aah, of course.. favicon request. Didn't thought of that. I really haven't done much server-side javascript with Node.js yet so all these little gotchas are biting me :/

SnapShot Over a year ago

I had something similar in a switch statement. The url.parse was outside the switch statement and some cases (like an xml format) did not return the params. As a result url.parse was undefined in those cases.

hyprstack Over a year ago

Is /favicon.ico always returned by default? Is there a way to avoid it?

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