将一级域名理解为 .com 或者 .com.cn 或者 .co.uk 等等
let addr1 = new URL("https://www.example.com/blahblah");
let addr2 = new URL("https://example.com/blahblah");
let addr3 = new URL("https://test.example.com/blahblah");
let addr4 = new URL("https://another.test.example.com/blahblah");
都需要取到二级域名 example.com
let addr1 = new URL("https://www.example.com.cn/blahblah");
let addr2 = new URL("https://example.com.cn/blahblah");
let addr3 = new URL("https://test.example.com.cn/blahblah");
let addr4 = new URL("https://another.test.example.com.cn/blahblah");
都需要取到二级域名 example.com.cn