js获取当前url，主机名和端口号

获取主机名：

var hostname = location.hostname;

获取端口号：

var  port = location.port;

获取主机名+端口号：

var host = location.host;

访问:172.16.0.1:30/login.html

hostname = 172.16.0.1;

port = 30;

host = 172.16.0.1/30;