URL 类
浏览器兼容的 URL 类，按照 WHATWG 网址标准实现。
解析网址的示例可以在标准本身中找到。
URL 类也在全局对象上可用。
按照浏览器的约定，URL 对象的所有属性都被实现为类原型上的获取器和设置器，而不是对象本身的数据属性。
因此，与旧版 urlObject 不同，在 URL 对象的任何属性上使用 delete 关键字（例如 delete myURL.protocol、delete myURL.pathname 等）没有任何作用，但仍会返回 true。
Browser-compatible URL class, implemented by following the WHATWG URL
Standard. Examples of parsed URLs may be found in the Standard itself.
The URL class is also available on the global object.
In accordance with browser conventions, all properties of URL objects
are implemented as getters and setters on the class prototype, rather than as
data properties on the object itself. Thus, unlike legacy urlObjects,
using the delete keyword on any properties of URL objects (e.g. delete myURL.protocol, delete myURL.pathname, etc) has no effect but will still
return true.