applyMiddleware.js
代码语言：javascript复制import compose from './compose'
/**
* Creates a store enhancer that applies middleware to the dispatch method
* of the Redux store. This is handy for a variety of tasks, such as expressing
* asynchronous actions in a concise manner, or logging every action payload.
*
* See `redux-thunk` package as an example of the Redux middleware.
*
* Because middleware is potentially asynchronous, this should be the first
* store enhancer in the composition chain.
*
* Note that each middleware will be given the `dispatch` and `getState` functions
* as named arguments.
*
* @param {...Function} middlewares The middleware chain to be applied.
* @returns {Function} A store enhancer applying the middleware.
*/
export default function applyMiddleware(...middlewares) {
return createStore => (...args) => {
// 创建一个store
const store = createStore(...args)
let dispatch = () => {
throw new Error(
`Dispatching while constructing your middleware is not allowed. `
`Other middleware would not be applied to this dispatch.`
)
}
const middlewareAPI = {
getState: store.getState,
dispatch: (...args) => dispatch(...args)
}
// 逐个执行插件，插件返回一个函数
const chain = middlewares.map(middleware => middleware(middlewareAPI))
// 链式执行，返回一个包装了假的dispatch的函数，假的dispatch也包装了dispatch或者假的dispatch
dispatch = compose(...chain)(store.dispatch)
return {
...store,
dispatch
}
}
}
/*
createStore(reducers, initState, applyMiddleware(middlewares))
applyMiddleware(middlewares)(createStore)(reducers, initState)
从21行开始执行
*/bindActionCreators.js
代码语言：javascript复制function bindActionCreator(actionCreator, dispatch) {
return function() {
return dispatch(actionCreator.apply(this, arguments))
}
}
/**
* Turns an object whose values are action creators, into an object with the
* same keys, but with every function wrapped into a `dispatch` call so they
* may be invoked directly. This is just a convenience method, as you can call
* `store.dispatch(MyActionCreators.doSomething())` yourself just fine.
*
* For convenience, you can also pass a single function as the first argument,
* and get a function in return.
*
* @param {Function|Object} actionCreators An object whose values are action
* creator functions. One handy way to obtain it is to use ES6 `import * as`
* syntax. You may also pass a single function.
*
* @param {Function} dispatch The `dispatch` function available on your Redux
* store.
*
* @returns {Function|Object} The object mimicking the original object, but with
* every action creator wrapped into the `dispatch` call. If you passed a
* function as `actionCreators`, the return value will also be a single
* function.
*/
/**
*
actionCreators = {
action1: function() {
return {
type: 'type1',
};
},
action2: function() {
return {
type: 'type2',
};
}
}
*/
export default function bindActionCreators(actionCreators, dispatch) {
if (typeof actionCreators === 'function') {
return bindActionCreator(actionCreators, dispatch)
}
if (typeof actionCreators !== 'object' || actionCreators === null) {
throw new Error(
`bindActionCreators expected an object or a function, instead received ${
actionCreators === null ? 'null' : typeof actionCreators
}. `
`Did you write "import ActionCreators from" instead of "import * as ActionCreators from"?`
)
}
const keys = Object.keys(actionCreators)
const boundActionCreators = {}
for (let i = 0; i < keys.length; i ) {
// action
const key = keys[i]
const actionCreator = actionCreators[key]
if (typeof actionCreator === 'function') {
boundActionCreators[key] = bindActionCreator(actionCreator, dispatch)
}
}
return boundActionCreators
}
/**
* boundActionCreators = {
action1: function() {
return dispatch(actionCreators[action1].apply(this, arguments))
},
action2: function() {
return dispatch(actionCreators[action2].apply(this, arguments))
}
}
*/combineReducers.js
代码语言：javascript复制import ActionTypes from './utils/actionTypes'
import warning from './utils/warning'
import isPlainObject from './utils/isPlainObject'
function getUndefinedStateErrorMessage(key, action) {
const actionType = action && action.type
const actionDescription =
(actionType && `action "${String(actionType)}"`) || 'an action'
return (
`Given ${actionDescription}, reducer "${key}" returned undefined. `
`To ignore an action, you must explicitly return the previous state. `
`If you want this reducer to hold no value, you can return null instead of undefined.`
)
}
function getUnexpectedStateShapeWarningMessage(
inputState,
reducers,
action,
unexpectedKeyCache
) {
const reducerKeys = Object.keys(reducers)
const argumentName =
action && action.type === ActionTypes.INIT
? 'preloadedState argument passed to createStore'
: 'previous state received by the reducer'
if (reducerKeys.length === 0) {
return (
'Store does not have a valid reducer. Make sure the argument passed '
'to combineReducers is an object whose values are reducers.'
)
}
if (!isPlainObject(inputState)) {
return (
`The ${argumentName} has unexpected type of "`
{}.toString.call(inputState).match(/s([a-z|A-Z] )/)[1]
`". Expected argument to be an object with the following `
`keys: "${reducerKeys.join('", "')}"`
)
}
const unexpectedKeys = Object.keys(inputState).filter(
key => !reducers.hasOwnProperty(key) && !unexpectedKeyCache[key]
)
unexpectedKeys.forEach(key => {
unexpectedKeyCache[key] = true
})
if (action && action.type === ActionTypes.REPLACE) return
if (unexpectedKeys.length > 0) {
return (
`Unexpected ${unexpectedKeys.length > 1 ? 'keys' : 'key'} `
`"${unexpectedKeys.join('", "')}" found in ${argumentName}. `
`Expected to find one of the known reducer keys instead: `
`"${reducerKeys.join('", "')}". Unexpected keys will be ignored.`
)
}
}
function assertReducerShape(reducers) {
Object.keys(reducers).forEach(key => {
const reducer = reducers[key]
const initialState = reducer(undefined, { type: ActionTypes.INIT })
// 传入的state是空的时候，reducer需要返回一个初始化的state，一个除undefined之外的值
if (typeof initialState === 'undefined') {
throw new Error(
`Reducer "${key}" returned undefined during initialization. `
`If the state passed to the reducer is undefined, you must `
`explicitly return the initial state. The initial state may `
`not be undefined. If you don't want to set a value for this reducer, `
`you can use null instead of undefined.`
)
}
// 处理非业务的action时必须返回当前传入的state，如果state是undefined则返回一个初始化的state，不能处理redux的action
if (
typeof reducer(undefined, {
type: ActionTypes.PROBE_UNKNOWN_ACTION()
}) === 'undefined'
) {
throw new Error(
`Reducer "${key}" returned undefined when probed with a random type. `
`Don't try to handle ${
ActionTypes.INIT
} or other actions in "redux/*" `
`namespace. They are considered private. Instead, you must return the `
`current state for any unknown actions, unless it is undefined, `
`in which case you must return the initial state, regardless of the `
`action type. The initial state may not be undefined, but can be null.`
)
}
})
}
/**
* Turns an object whose values are different reducer functions, into a single
* reducer function. It will call every child reducer, and gather their results
* into a single state object, whose keys correspond to the keys of the passed
* reducer functions.
*
* @param {Object} reducers An object whose values correspond to different
* reducer functions that need to be combined into one. One handy way to obtain
* it is to use ES6 `import * as reducers` syntax. The reducers may never return
* undefined for any action. Instead, they should return their initial state
* if the state passed to them was undefined, and the current state for any
* unrecognized action.
*
* @returns {Function} A reducer function that invokes every reducer inside the
* passed object, and builds a state object with the same shape.
*/
/**
*
* reducers = {
* reducer1: function(state, action) {
switch (action.type) {
case 'action1':
return newState
default:
return newState
}
},
* reducer2: function(state, action) {
switch (action.type) {
case 'action1':
return newState
default:
return newState
}
}
*/
export default function combineReducers(reducers) {
const reducerKeys = Object.keys(reducers)
// 报存过滤后的reducers
const finalReducers = {}
for (let i = 0; i < reducerKeys.length; i ) {
const key = reducerKeys[i]
if (process.env.NODE_ENV !== 'production') {
if (typeof reducers[key] === 'undefined') {
warning(`No reducer provided for key "${key}"`)
}
}
if (typeof reducers[key] === 'function') {
finalReducers[key] = reducers[key]
}
}
const finalReducerKeys = Object.keys(finalReducers)
let unexpectedKeyCache
if (process.env.NODE_ENV !== 'production') {
unexpectedKeyCache = {}
}
let shapeAssertionError
try {
assertReducerShape(finalReducers)
} catch (e) {
shapeAssertionError = e
}
// 返回聚合reducer的函数
return function combination(state = {}, action) {
if (shapeAssertionError) {
throw shapeAssertionError
}
if (process.env.NODE_ENV !== 'production') {
const warningMessage = getUnexpectedStateShapeWarningMessage(
state,
finalReducers,
action,
unexpectedKeyCache
)
if (warningMessage) {
warning(warningMessage)
}
}
let hasChanged = false
const nextState = {}
// 遍历所有的reducer
for (let i = 0; i < finalReducerKeys.length; i ) {
const key = finalReducerKeys[i]
// 取得当前的reducer
const reducer = finalReducers[key]
// 根据reducer对应的键，取得当前reducer对应的state子树
const previousStateForKey = state[key]
// 执行当前reducer
const nextStateForKey = reducer(previousStateForKey, action)
if (typeof nextStateForKey === 'undefined') {
const errorMessage = getUndefinedStateErrorMessage(key, action)
throw new Error(errorMessage)
}
// 更新子树
nextState[key] = nextStateForKey
// 判断当前reducer对应的子树是否已被更新，即不是同一个对象
hasChanged = hasChanged || nextStateForKey !== previousStateForKey
}
// 如果有子树被修改则返回新的state，否则返回旧的state。不直接返回nextState是为了避免rerender，因为即使nextState和state的内容是一样的，但是地址不一样了
return hasChanged ? nextState : state
}
}compose.js
代码语言：javascript复制/**
* Composes single-argument functions from right to left. The rightmost
* function can take multiple arguments as it provides the signature for
* the resulting composite function.
*
* @param {...Function} funcs The functions to compose.
* @returns {Function} A function obtained by composing the argument functions
* from right to left. For example, compose(f, g, h) is identical to doing
* (...args) => f(g(h(...args))).
*/
// 从右往左执行函数
export default function compose(...funcs) {
// 没传参数
if (funcs.length === 0) {
return arg => arg
}
// 传了一个
if (funcs.length === 1) {
return funcs[0]
}
// 传了多个。原理：把前n个函数（一开始是第一第二个函数）封装成一个函数fn，fn再和下一个函数封装成fn1，以此类推
return funcs.reduce((a, b) => (...args) => a(b(...args)))
}createStore.js
代码语言：javascript复制import $$observable from 'symbol-observable'
import ActionTypes from './utils/actionTypes'
import isPlainObject from './utils/isPlainObject'
/**
* 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`.
*
* @param {Function} reducer A function that returns the next state tree, given
* the current state tree and the action to handle.
*
* @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 {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()`.
*
* @returns {Store} A Redux store that lets you read the state, dispatch actions
* and subscribe to changes.
*/
export default function createStore(reducer, preloadedState, enhancer) {
// enhancer只能有一个
if (
(typeof preloadedState === 'function' && typeof enhancer === 'function') ||
(typeof enhancer === 'function' && typeof arguments[3] === 'function')
) {
throw new Error(
'It looks like you are passing several store enhancers to '
'createStore(). This is not supported. Instead, compose them '
'together to a single function'
)
}
// 可能是只传了两个参数，或者传了三个，单但第二个是函数第三个是undefined，则修正参数
if (typeof preloadedState === 'function' && typeof enhancer === 'undefined') {
enhancer = preloadedState
preloadedState = undefined
}
// 如果传了enhancer并且是个函数，则直接执行enhancer，并且返回，enhancer一般是applyMiddleware(...args)返回的函数，见applyMiddleware.js
if (typeof enhancer !== 'undefined') {
if (typeof enhancer !== 'function') {
throw new Error('Expected the enhancer to be a function.')
}
return enhancer(createStore)(reducer, preloadedState)
}
if (typeof reducer !== 'function') {
throw new Error('Expected the reducer to be a function.')
}
let currentReducer = reducer
let currentState = preloadedState
let currentListeners = []
let nextListeners = currentListeners
let isDispatching = false
// 如果指向一样则复制一份
function ensureCanMutateNextListeners() {
if (nextListeners === currentListeners) {
nextListeners = currentListeners.slice()
}
}
/**
* Reads the state tree managed by the store.
*
* @returns {any} The current state tree of your application.
*/
function getState() {
if (isDispatching) {
throw new Error(
'You may not call store.getState() while the reducer is executing. '
'The reducer has already received the state as an argument. '
'Pass it down from the top reducer instead of reading it from the store.'
)
}
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.
*
* You may call `dispatch()` from a change listener, with the following
* caveats:
*
* 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.
*
* 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.
*
* @param {Function} listener A callback to be invoked on every dispatch.
* @returns {Function} A function to remove this change listener.
*/
// 订阅dispatch事件
function subscribe(listener) {
if (typeof listener !== 'function') {
throw new Error('Expected the listener to be a function.')
}
if (isDispatching) {
throw new Error(
'You may not call store.subscribe() while the reducer is executing. '
'If you would like to be notified after the store has been updated, subscribe from a '
'component and invoke store.getState() in the callback to access the latest state. '
'See https://redux.js.org/api-reference/store#subscribe(listener) for more details.'
)
}
let isSubscribed = true
/*
确保nextListeners是新的数组，每次修改的时候保证不修改当前的listen队列，先放到nextListeners中，
nextListeners类似一个缓存队列，等listen队列执行完后，下次执行后队列内容会同步过去
*/
ensureCanMutateNextListeners()
nextListeners.push(listener)
// 返回取消订阅函数
return function unsubscribe() {
// 防止重入，误删数据
if (!isSubscribed) {
return
}
if (isDispatching) {
throw new Error(
'You may not unsubscribe from a store listener while the reducer is executing. '
'See https://redux.js.org/api-reference/store#subscribe(listener) for more details.'
)
}
isSubscribed = false
// 同上，操作队列的时候先在缓存队列上操作
ensureCanMutateNextListeners()
const index = nextListeners.indexOf(listener)
nextListeners.splice(index, 1)
}
}
/**
* Dispatches an action. It is the only way to trigger a state change.
*
* 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.
*
* 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.
*
* @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.
*
* @returns {Object} For convenience, the same action object you dispatched.
*
* Note that, if you use a custom middleware, it may wrap `dispatch()` to
* return something else (for example, a Promise you can await).
*/
// 分发action
function dispatch(action) {
if (!isPlainObject(action)) {
throw new Error(
'Actions must be plain objects. '
'Use custom middleware for async actions.'
)
}
if (typeof action.type === 'undefined') {
throw new Error(
'Actions may not have an undefined "type" property. '
'Have you misspelled a constant?'
)
}
if (isDispatching) {
throw new Error('Reducers may not dispatch actions.')
}
// 执行reducer
try {
isDispatching = true
currentState = currentReducer(currentState, action)
} finally {
isDispatching = false
}
// 把缓存队列的数据同步到当前队列，执行每个订阅者的函数
const listeners = (currentListeners = nextListeners)
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.
*
* 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.
*
* @param {Function} nextReducer The reducer for the store to use instead.
* @returns {void}
*/
function replaceReducer(nextReducer) {
if (typeof nextReducer !== 'function') {
throw new Error('Expected the nextReducer to be a function.')
}
currentReducer = nextReducer
dispatch({ type: ActionTypes.REPLACE })
}
/**
* 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
*/
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.
*/
subscribe(observer) {
if (typeof observer !== 'object' || observer === null) {
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.
dispatch({ type: ActionTypes.INIT })
return {
dispatch,
subscribe,
getState,
replaceReducer,
[$$observable]: observable
}
}
