After refreshing the page, the server stops working, why?

var router = require("./router.js")
// problem : we need a simple way to look at user's badge count and JavaScript point from a web browser
// solution : use node.js to perfom the profile look ups and server our template via HTTP

// create a web server 
var http = require('http')
http.createServer(function (request, response) {
    router.home(request, response)
    router.user(request, response)
}).listen(3000)
console.log('server running at http://127.0.0.1:3000/')


// function that handles the reading of files and merge in value
//    read from file and get a string 
//      merge values in to string

var Profile = require("./profile.js")
// handle HTTP route GET / and POST / ie Home
function home(request, response) {
// if url == "/" && GET 
if (request.url === "/") {

//    show search
    response.writeHead(200, {'Content-Type': 'text/plain'})
    response.write("Header\n")
    response.write("Search\n")
    response.end('Footer\n')

// if url == "/" && POST 
//    redirect to /:username 
}
}

// handle HTTP route GET /:username ie /chalkers
function user(request, response) {
// if url = "/...."
var username = request.url.replace("/", "")
    if (username.length > 0) {
    response.writeHead(200, {'Content-Type': 'text/plain'})
    response.write("Header \n")
    response.write(username + "\n")
    response.end('Footer\n')
    }
//  get json from Trehouse
//    on "end"
//      show profile 
//    on "error" 
//      show error
}

module.exports.home = home
module.exports.user - user