module--URL

url 包提供了三个方法
假设url字符串为：'http://user:pass@host.com:8080/p/a/t/h?query=string#hash'

一、url.parse(urlStr, [parseQueryString], [slashesDenoteHost]）

按url规则拆解urlStr字符串，接收三个参数

1. urlStr， url字符串(必传)
2. parseQueryString， bool类型， 默认值false。 对url中query部分解析后输出格式的选择， true的话输出格式由默认的 'query=string' 转为对象格式{ query: 'string' }
3. slashesDenoteHost, bool类型， 默认值false。

parse解析获取的对象的结构，这个对认识url的组成也是极好的：

href: The full URL that was originally parsed. Both the protocol and host are lowercased.

  Example: 'http://user:pass@host.com:8080/p/a/t/h?query=string#hash'

protocol: The request protocol, lowercased.

  Example: 'http:'

slashes: The protocol requires slashes after the colon

  Example: true or false

host: The full lowercased host portion of the URL, including port information.

  Example: 'host.com:8080'

auth: The authentication information portion of a URL.

  Example: 'user:pass'

hostname: Just the lowercased hostname portion of the host.

 Example: 'host.com'

port: The port number portion of the host.

  Example: '8080'

pathname: The path section of the URL, that comes after the host and before the query, including the initial slash if present.

  Example: '/p/a/t/h'

search: The 'query string' portion of the URL, including the leading question mark.

  Example: '?query=string'

path: Concatenation of pathname and search.

  Example: '/p/a/t/h?query=string'

query: Either the 'params' portion of the query string, or a querystring-parsed object.

  Example: 'query=string' or {'query':'string'}

hash: The 'fragment' portion of the URL including the pound-sign.

  Example: '#hash'

二、 url.format(urlObj)

parse的反用，将对象解析成url字符串

三、 url.resolve(from, to)

为URL或 href 插入 或 替换原有的标签

var url = require('url');
var a = url.resolve('/one/two/three', 'four') ,
b = url.resolve('http://example.com/', '/one'),
c = url.resolve('http://example.com/one', '/two');
console.log(a +","+ b +","+ c);
//输出结果：
///one/two/four
//http://example.com/one
//http://example.com/two