react-redux的store实现

store的方法:

• store.getState()
• store.dispatch()
• store.subscribe()

import { createStore } from 'redux';
let { subscribe, dispatch, getState } = createStore(reducer);
createStore方法还可以接受第二个参数，表示 State 的最初状态。这通常是服务器给出的。

const createStore = (reducer) => {
  let state;
  let listeners = [];

  const getState = () => state;

  const dispatch = (action) => {
    state = reducer(state, action);
    listeners.forEach(listener => listener());
  };

  const subscribe = (listener) => {
    listeners.push(listener);
    return () => {
      listeners = listeners.filter(l => l !== listener);
    }
  };

  dispatch({});

  return { getState, dispatch, subscribe };
};