access node.js server from domain name

I'm learning Node.js can created a hello world server, here is the code server.js

var http = require("http");

http.createServer(function(request, response) {
    response.writeHead(200, {"Content-Type": "text/plain"});
    response.write("Hello World");
    response.end();
}).listen(8888);

I can access localhost:8888 from my server machine but I can't access ip:8888 from another machine and I also can't access domainname:8888. What is the problem?