Localhost无法连接节点js

Question

我刚刚安装了节点。我遵循了它的入门指南并运行文件。这是文件：

const http = require('http');

const hostname = '127.0.0.1';
const port = 3000;

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World\n');
});

server.listen(3000, "localhost", () => {
  console.log(`Server running at http://${localhost}:${3000}/`);
});

在firefox上运行localhost：3000后，它说无法连接。