http://lmgtfy.com/?q=nodejs+%E6%96%87%E4%BB%B6%E6%9C%8D%E5%8A%A1%E5%99%A8

var http = require("http"),
    url  = require("url"),
    path = require("path"),
    fs   = require("fs");

http.createServer(function (req, res) {
    var pathname=__dirname+url.parse(req.url).pathname;
    if (path.extname(pathname)=="") {
        pathname+="/";
    }
    if (pathname.charAt(pathname.length-1)=="/"){
        pathname+="index.html";
    }

    path.exists(pathname,function(exists){
        if(exists){
            switch(path.extname(pathname)){
                case ".html":
                    res.writeHead(200, {"Content-Type": "text/html"});
                    break;
                case ".js":
                    res.writeHead(200, {"Content-Type": "text/javascript"});
                    break;
                case ".css":
                    res.writeHead(200, {"Content-Type": "text/css"});
                    break;
                case ".gif":
                    res.writeHead(200, {"Content-Type": "image/gif"});
                    break;
                case ".jpg":
                    res.writeHead(200, {"Content-Type": "image/jpeg"});
                    break;
                case ".png":
                    res.writeHead(200, {"Content-Type": "image/png"});
                    break;
                default:
                    res.writeHead(200, {"Content-Type": "application/octet-stream"});
            }

            fs.readFile(pathname,function (err,data){
                res.end(data);
            });
        } else {
            res.writeHead(404, {"Content-Type": "text/html"});
            res.end("<h1>404 Not Found</h1>");
        }
    });

}).listen(8080, "127.0.0.1");

console.log("Server running at http://127.0.0.1:8080/");

参考：http://nodejs.org/api/http.html

var url  = require("url"),
     fs=require("fs"),
     http=require("http"),
     path = require("path");
http.createServer(function (req, res) {
    var pathname=__dirname+url.parse(req.url).pathname;
    if (path.extname(pathname)=="") {
        pathname+="/";
    }
    if (pathname.charAt(pathname.length-1)=="/"){
        pathname+="index.html";
    }

    fs.exists(pathname,function(exists){
        if(exists){
            switch(path.extname(pathname)){
                case ".html":
                    res.writeHead(200, {"Content-Type": "text/html"});
                    break;
                case ".js":
                    res.writeHead(200, {"Content-Type": "text/javascript"});
                    break;
                case ".css":
                    res.writeHead(200, {"Content-Type": "text/css"});
                    break;
                case ".gif":
                    res.writeHead(200, {"Content-Type": "image/gif"});
                    break;
                case ".jpg":
                    res.writeHead(200, {"Content-Type": "image/jpeg"});
                    break;
                case ".png":
                    res.writeHead(200, {"Content-Type": "image/png"});
                    break;
                default:
                    res.writeHead(200, {"Content-Type": "application/octet-stream"});
            }

            fs.readFile(pathname,function (err,data){
                res.end(data);
            });
        } else {
            res.writeHead(404, {"Content-Type": "text/html"});
            res.end("<h1>404 Not Found</h1>");
        }
    });
}).listen(8080, "127.0.0.1");
console.log("Server running at http://127.0.0.1:8080/");

path没有exists这个API啊，楼上的代码有问题，这个是没问题的。