如果看不清楚,可以查看https://segmentfault.com/a/1190000018385942
import isPlainObject from 'lodash/isPlainObject'
import $$observable from 'symbol-observable'
/**
* These are private action types reserved by Redux.
* For any unknown actions, you must return the current state.
* If the current state is undefined, you must return the initial state.
* Do not reference these action types directly in your code.
*
* 这些都是redux本身预置的私有action types
* 对于任何未知的action, 你一定要return当前的state.
* 如果当前的state是undefined, 你一定要return最初始的state.
* 一定,一定,一定不要在代码中直接引用action types .
*/
export const ActionTypes = { //初始化action的type,没有action参数的时候用
INIT: '@@redux/INIT'
}
/**
* Creates a Redux store that holds the state tree.
* The only way to change the data in the store is to call `dispatch()` on it.
* There should only be a single store in your app. To specify how different
* parts of the state tree respond to actions, you may combine several reducers
* into a single reducer function by using `combineReducers`.
*
* 创建一个包含state tree(状态树)的redux store.
* 唯一改变store中data(数据)的方法是调用`dispatch()`方法.
* 在你的程序中应该只存在唯一一个store, 来表明state tree各部分怎样对action做出反应
* 你可能需要将多个reducer用`combineReducers`组合在一起
*
* @param {Function} reducer A function that returns the next state tree, given
* the current state tree and the action to handle.
*
* @param {Function} reducer 参数reducer是一个返回下一个state tree(状态树)的函数,来操作当前的state和action
*
* @param {any} [preloadedState] The initial state. You may optionally specify it
* to hydrate the state from the server in universal apps, or to restore a
* previously serialized user session.
* If you use `combineReducers` to produce the root reducer function, this must be
* an object with the same shape as `combineReducers` keys.
*
* @param {any} [preloadedState] 初始化的state,可选参数,你可以在universal(一般的,普遍的,我不知道怎么说比较合适)
* 的程序中与服务器的state结合,或者restore一个预先连续的user session(直译过来的,一般用不到)
* 如果你用`combineReducers`产生一个根reducer函数,这一定是一个和`combineReducers`的key一样的对象(根reducer是一个对象)
*
* @param {Function} [enhancer] The store enhancer. You may optionally specify it
* to enhance the store with third-party capabilities such as middleware,
* time travel, persistence, etc. The only store enhancer that ships with Redux
* is `applyMiddleware()`.
*
* @param {Function} [enhancer] store增强器. 可选参数.用来增强第三方库的能力集(这个词是直译),
* 比如中间件,时空穿越,和持续性(也是直译).redux的store增强器是`applyMiddleware()`
*
* @returns {Store} A Redux store that lets you read the state, dispatch actions
* and subscribe to changes.
*
* @returns {Store} 返回值 一个redux的store,让你可以读取state, dispatch actions 和订阅更改
*/
//createStore的目的只是创建一个store,这个store包含5个方法(一般只用到3个,最常用的是dispatch)
export default function createStore(reducer, preloadedState, enhancer) {
if (typeof preloadedState === 'function' && typeof enhancer === 'undefined') {
enhancer = preloadedState
preloadedState = undefined
}
if (typeof enhancer !== 'undefined') {
if (typeof enhancer !== 'function') {
throw new Error('Expected the enhancer to be a function.')//期望enhancer是个函数
}
// 当enhancer是函数的时候返回,然后执行,并将createStore作为参数传入,然后createStore就在 //enhancer里面去执行了
return enhancer(createStore)(reducer, preloadedState)
}
if (typeof reducer !== 'function') {
throw new Error('Expected the reducer to be a function.')
}
let currentReducer = reducer //一般此reducer不是单个的reducer函数,而是combineReducers函数
let currentState = preloadedState
let currentListeners = [] //监听函数
let nextListeners = currentListeners
let isDispatching = false
function ensureCanMutateNextListeners() { //nextListeners不是currentListeners
if (nextListeners === currentListeners) {
nextListeners = currentListeners.slice()
}
}
/**
* Reads the state tree managed by the store.
*
* 读取被store管理的state树
*
* @returns {any} The current state tree of your application.
*
*返回你的程序的当前的state树
*/
function getState() {
return currentState
}
/**
* Adds a change listener. It will be called any time an action is dispatched,
* and some part of the state tree may potentially have changed. You may then
* call `getState()` to read the current state tree inside the callback.
*
* 添加一个改变事件,任何时候一个action被dispatch这个事件就会被调用,然后state树的某一部分就
* 会改变. 你也可以在回调函数里面调用`getState()`来查看当前的state树
*
* You may call `dispatch()` from a change listener, with the following
* caveats:
*
* 以下几种情况你也可以调用`dispatch()`
*
* 1. The subscriptions are snapshotted just before every `dispatch()` call.
* If you subscribe or unsubscribe while the listeners are being invoked, this
* will not have any effect on the `dispatch()` that is currently in progress.
* However, the next `dispatch()` call, whether nested or not, will use a more
* recent snapshot of the subscription list.
*
* 每次调用`dispatch`之前,订阅都会被snapshot,
* 当事件被触发的时候你订阅或者不订阅,在当前的进程中都不会对`dispatch`有什么影响
* 然而当下一次`dispatch`被调用时,无论嵌套与否,将会使用最近的订阅列表的snapshot
*
* 2. The listener should not expect to see all state changes, as the state
* might have been updated multiple times during a nested `dispatch()` before
* the listener is called. It is, however, guaranteed that all subscribers
* registered before the `dispatch()` started will be called with the latest
* state by the time it exits.
*
* 不要期待监听事件可以看到所有的状态改变,因为在事件被调用前,state在嵌套的`dispatch`间
* 可能已经更新了很多次
*
* @param {Function} listener A callback to be invoked on every dispatch.
* 每次dispatch都会被出发的回调函数
*
* @returns {Function} A function to remove this change listener.
* 返回一个移除该事件的函数
*/
function subscribe(listener) {
if (typeof listener !== 'function') {
throw new Error('Expected listener to be a function.')
}
let isSubscribed = true
ensureCanMutateNextListeners()
nextListeners.push(listener) //添加事件到nextListeners数组
return function unsubscribe() {
if (!isSubscribed) {
return
}
isSubscribed = false
ensureCanMutateNextListeners()
const index = nextListeners.indexOf(listener)
nextListeners.splice(index, 1) //从nextListeners数组中移除事件
}
}
/**
* Dispatches an action. It is the only way to trigger a state change.
*
* dispatch action是唯一触发state改变的途径
*
* The `reducer` function, used to create the store, will be called with the
* current state tree and the given `action`. Its return value will
* be considered the **next** state of the tree, and the change listeners
* will be notified.
*
* `reducer`函数,被用来创建store,有当前的state树和action就会被调用(state和action是reducer函数的参数)
* 它的返回值会被当做下一个state树.监听事件会注意到state树的改变
*
* The base implementation only supports plain object actions. If you want to
* dispatch a Promise, an Observable, a thunk, or something else, you need to
* wrap your store creating function into the corresponding middleware. For
* example, see the documentation for the `redux-thunk` package. Even the
* middleware will eventually dispatch plain object actions using this method.
*
* 最基本的用法是仅支持 为纯对象的 action,如果你想要dispatch一个promise,一个Observable,
* thunk,或是其他东西,你需要封装store创建一个进入到相应中间件的函数. 比如,看一个`redux-thunk`
* 的文档,即使是中间件最终也会用这个方法dispatch 纯对象的action
*
* @param {Object} action A plain object representing “what changed”. It is
* a good idea to keep actions serializable so you can record and replay user
* sessions, or use the time travelling `redux-devtools`. An action must have
* a `type` property which may not be `undefined`. It is a good idea to use
* string constants for action types.
*
* action是一个纯对象,代表'什么被改变了'. 保持action的连续性是个好主意,这样你就可以记录和
* 重现user session,或者使用时空穿梭`redux-devtools`.
* action必须包含一个`type`属性,即使是`undefined`. 通常使用字符串常量表示
*
* @returns {Object} For convenience, the same action object you dispatched.
*
* 为了方便,返回你dispatch的action
*
* Note that, if you use a custom middleware, it may wrap `dispatch()` to
* return something else (for example, a Promise you can await).
* 注意 如果你想使用特定的中间件,可封装`dispatch`返回其他东西(比如, 一个异步调用的promise)
*
*/
function dispatch(action) {
if (!isPlainObject(action)) {
throw new Error(
'Actions must be plain objects. ' +
'Use custom middleware for async actions.'
) //actions必须为纯对象,使用特定中间件异步调用actions
}
if (typeof action.type === 'undefined') {
throw new Error(
'Actions may not have an undefined "type" property. ' +
'Have you misspelled a constant?'
) //actions可能有一个未定义的type属性,你可能拼错了这个常量
}
if (isDispatching) {
throw new Error('Reducers may not dispatch actions.')//reducer没有dispatch action
}
try {
isDispatching = true
//dispatch的目的就是改变currentState
currentState = currentReducer(currentState, action) //currentReducer = reducer
} finally {
isDispatching = false
}
const listeners = currentListeners = nextListeners //订阅函数的事件
for (let i = 0; i < listeners.length; i++) {
const listener = listeners[i]
listener()
}
return action
}
/**
* Replaces the reducer currently used by the store to calculate the state.
*
* 替换 store 当前用来计算 state 的 reducer。
*
* You might need this if your app implements code splitting and you want to
* load some of the reducers dynamically. You might also need this if you
* implement a hot reloading mechanism for Redux.
*
* 这是一个高级 API。只有在你需要实现代码分隔，而且需要立即加载一些 reducer 的时候才可能会用到它。
*在实现 Redux 热加载机制的时候也可能会用到
*
* @param {Function} nextReducer The reducer for the store to use instead.
* store所替换的reducer
* @returns {void}
*/
function replaceReducer(nextReducer) {
if (typeof nextReducer !== 'function') {
throw new Error('Expected the nextReducer to be a function.')
}
currentReducer = nextReducer
dispatch({ type: ActionTypes.INIT })
}
/**
* Interoperability point for observable/reactive libraries.
* @returns {observable} A minimal observable of state changes.
* For more information, see the observable proposal:
* https://github.com/tc39/proposal-observable
*
* observable/reactive库的互用性
* observable是一个mini的 可观察state的改变
* 在下面这个网址查看更多observable的信息
*/
function observable() {
const outerSubscribe = subscribe
return {
/**
* The minimal observable subscription method.
* @param {Object} observer Any object that can be used as an observer.
* The observer object should have a `next` method.
* @returns {subscription} An object with an `unsubscribe` method that can
* be used to unsubscribe the observable from the store, and prevent further
* emission of values from the observable.
*
* mini的可观察订阅的方法
* observer是 任何对象都可以用作观察者,这个观察者应该有一个`next`方法
* subscription 一个有`unsubscribe`方法的对象.可以用做退订observable,防止进一步发出value值
* (我也不知道什么意思,外国人说话比较随意)
*/
subscribe(observer) {
if (typeof observer !== 'object') {
throw new TypeError('Expected the observer to be an object.')
}
function observeState() {
if (observer.next) {
observer.next(getState())
}
}
observeState()
const unsubscribe = outerSubscribe(observeState)
return { unsubscribe }
},
[$$observable]() {
return this
}
}
}
// When a store is created, an "INIT" action is dispatched so that every
// reducer returns their initial state. This effectively populates
// the initial state tree.
/**
* 当创建一个store的时候,一个初始的action就被dispatch了,所以每个reducer都会返回初始的state
* 这个可以很高效的得到state树
*/
dispatch({ type: ActionTypes.INIT })
return {
dispatch,
subscribe,
getState,
replaceReducer,
[$$observable]: observable
}
}
