1.redux is not react-redux, is used for managing global states.
2.how redux works
a.UI event create a redux action which is an object includes type:event and data
b.new action will be dispatched to store object
c.store object stores existing object, if this the first time without existing state. reducer will create one
d.reducer manipulate existing state based on passed action
e.finally, generate a new state then notify all subscribe components
3.wirte calculator app using raw react
4.rewrite example above using redux without action creator
a.store.js
b.reducer.js
5.rewrite exmaple above using redux with action creator
a.countAction.js
b.constant.js
6.rewrite example above using async action creator
