我正在阅读出色的在线书籍http://nodebeginner.org/，并尝试了简单的代码

var http = require("http");

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

http.createServer(onRequest).listen(8888);

现在我不知道（而且我仍然不知道！）如何优雅地关闭node.js，所以我就去了ctrl+z。现在，每次我尝试运行时node server.js，都会收到以下错误消息。

node.js:134
        throw e; // process.nextTick error, or 'error' event on first tick
        ^
Error: EADDRINUSE, Address already in use
    at Server._doListen (net.js:1100:5)
    at net.js:1071:14
    at Object.lookup (dns.js:153:45)
    at Server.listen (net.js:1065:20)
    at Object.<anonymous> (/Users/Bob/server.js:7:4)
    at Module._compile (module.js:402:26)
    at Object..js (module.js:408:10)
    at Module.load (module.js:334:31)
    at Function._load (module.js:293:12)
    at Array.<anonymous> (module.js:421:10)

因此，有两个问题：

1）如何正常关闭node.js？

2）如何修复我创建的混乱？