combindReducer源码解析

function combindReducer(reducers) {
//过滤掉不是function 的reducer
  const reducerKeys = Object.keys(reducers)
  const finalReducers = {}
  reducerKeys.forEach((key) => {
      if(typeof reducers[key] === 'function') {
      finalReducers[key] = reducers[key]
      } 
  })
  const finalReducersKeys = Object.keys(finalReducers)
    let hasChange = false;
    const nextState = {};
    return function combind(state={}, action) {
        finalReducersKeys.forEach((key) => {
            const previousValue = state[key];
            const nextValue = reducers[key](previousValue, action);
            nextState[key] = nextValue;
            hasChange = hasChange || previousValue !== nextValue
        })
        return hasChange ? nextState : state;
    }
}