node中加载静态资源css，js等不显示问题

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

var server = http.createServer();

var handlerequest = function(request,respone){
var url = request.url;
// respone.writeHead(200,{'Content-Type':'text/html'});
if(url=='/'){
respone.writeHead(200,{'Content-Type':'text/html'});
var ns = fs.readFile('./index.html', function(err, data) {
if (err) {
console.error(err);
return;
}
respone.end(data);
});
//respone.end();
}else if(url != '/'){
var surl = '.'+url;
var type = surl.substr(surl.lastIndexOf(".")+1,surl.length)
respone.writeHead(200,{'Content-type':"text/"+type});
// respone.writeHead(200,{'Content-Type':'text/css'});
var ns = fs.readFile(surl, function(err, data) {
if (err) {
console.error(err);
return;
}
respone.end(data);
});
}
}
server.on('request',handlerequest);

server.listen(3000,function(){
console.log("runing...");
})