2 行代码的 replaceReducer

reducer 拆分后，和组件是一一对应的。我们就希望在做按需加载的时候，reducer也可以跟着组件在必要的时候再加载，然后用新的 reducer 替换老的 reducer。

const createStore = function (reducer, initState) {
  ...
  function replaceReducer(nextReducer) {
    reducer = nextReducer
    /*刷新一遍 state 的值，新来的 reducer 把自己的默认状态放到 state 树上去*/
    dispatch({ type: Symbol() })
  }
  ...
  return {
    ...
    replaceReducer
  }
}

我们来尝试使用下

const reducer = combineReducers({
  counter: counterReducer
});
const store = createStore(reducer);
/*生成新的reducer*/
const nextReducer = combineReducers({
  counter: counterReducer,
  info: infoReducer
});
/*replaceReducer*/
store.replaceReducer(nextReducer);

replaceReducer 示例源码见 demo-5