createStore

返回一个对象：

• dispatch：分发一个action
• getState：得到仓库中当前的状态
• subscribe：注册一个监听器，监听器是一个无参函数，该分发一个action之后，会运行注册的监听器。该函数会返回一个函数，用于取消监听

/**
 * 
 * @param {*} obj  对象
 * @returns  判断是否是平面对象
 */
function isPlainObject(obj) {
    if (typeof obj !== 'object') {
        return false;
    }
    return Object.getPrototypeOf(obj) === Object.prototype;
}
/**
 * 
 * @param {*} length 
 */
function RandomStr(length) {
    return Math.random().toString(36).substr(2, length).split('').join('.')
}
/**
 * 
 * @param {*} reducer 
 * @param {*} defaultState 
 * @returns 
 */
export default function (reducer, defaultState) {
    let currState = defaultState,
        currReducer = reducer;
    const listeners = [];
    function dispatch(action) {
        // 判断action是平面对象
        if (!isPlainObject(action)) {
            throw TypeError('action must be a plain objet')
        }
        if (action.type === undefined) {
            throw TypeError('action must be have property of type')
        }
        currState = currReducer(currState, action);
        for (const listener of listeners) {
            listener();
        }
    }
    function getState() {
        return currState;
    }
    function subscribe(listener) {
        listeners.push(listener);
        let isRemove = false;
        return function () {
            if (isRemove) {
                return;
            }
            const index = listeners.indexOf(listener);
            listeners.splice(index, 1);
            isRemove = true;
            console.log('listeners', listeners)
        }
    }
    dispatch({
        type: `@@redux/INIT${RandomStr()}`
    })
    return {
        dispatch,
        getState,
        subscribe
    }
}