react-router 实现原理

参考： 

https://segmentfault.com/a/1190000007166839

http://zhenhua-lee.github.io/react/history.html

一、共有多少种 router 实现

exports.createBrowserHistory = _createBrowserHistory3.default;

exports.createHashHistory = _createHashHistory3.default;

exports.createMemoryHistory = _createMemoryHistory3.default

二、原理

1、hashchange

2、 pushState, replaceState, and the popstate event.

3、Creates a history object that stores locations in memory.