How to starting a basic nodejs server?

I am learning nodejs to develop a app of mine. So I'm starting with the basic of the basic : creating a node server.

Here is the code :

var http = require(http);

http.createServer(function(req,res){

res.writeHead(200, {'content-type':'text/plain'});
res.end('Hello world');
}).listen(9001);

console.log('server is running on port 9001');

and what my console returned to me

gdiop@localhost:~/Desktop/learning/node.js> node index.js

assert.js:81
  throw new assert.AssertionError({
  ^
AssertionError: missing path
    at Module.require (module.js:495:3)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (/home/gdiop/Desktop/learning/node.js/index.js:1:74)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.runMain (module.js:604:10)
    at run (bootstrap_node.js:393:7)
gdiop@localhost:~/Desktop/learning/node.js> 

Am I missing something here ... ?

via Gabriel D.