middleware

什么是middleware，个人理解就是一个可以让你在dispatch action的时候，可以同时做几个动作，比如想打印日志，异步请求

middleware运行

middleware logger

export const logger = store => next => action = {
  console.log(1111)
  next(action)
  console.log(2222)
}

export const logger1 = store => next => action = {
  console.log(333333)
  next(action)
  console.log(44444)
}

运行

const dispatch_1 = applyMiddleware([logger, logger1])

dispatch_1 = logger(logger1(store.dispatch))

这是执行dispatch(action)的时候 第一步就是执行logger函数 1，打印出1111 2，执行logger1(store.dispatch)(action) 3, 打印出333 4，执行store.dispatch(action) 4，打印出222 5，打印出 4444