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代码也很少。
function dispatch(action: A) {
if (!isPlainObject(action)) {
throw new Error(
`Actions must be plain objects. Instead, the actual type was: '${
kindOf(
action
)}'. You may need to add middleware to your store setup to handle dispatching other values, such as 'redux-thunk' to handle dispatching functions. See https://redux.js.org/tutorials/fundamentals/part-4-store#middleware and https://redux.js.org/tutorials/fundamentals/part-6-async-logic#using-the-redux-thunk-middleware for examples.`
)
}
if (typeof action.type === 'undefined') {
throw new Error(
'Actions may not have an undefined "type" property. You may have misspelled an action type string constant.'
)
}
if (isDispatching) {
throw new Error('Reducers may not dispatch actions.')
}
try {
isDispatching = true
currentState = currentReducer(currentState, action)
} finally {
isDispatching = false
}
const listeners = (currentListeners = nextListeners)
for (let i = 0; i < listeners.length; i++) {
const listener = listeners[i]
listener()
}
return action
}
1，如果参数不是简单的对象，报错。
何为简单的对象？
原型为null，由字面量声明。
这种算法适用性更广。
if (!isPlainObject(action)) {
throw new Error(
`Actions must be plain objects. Instead, the actual type was: '${
kindOf(
action
)}'. You may need to add middleware to your store setup to handle dispatching other values, such as 'redux-thunk' to handle dispatching functions. See https://redux.js.org/tutorials/fundamentals/part-4-store#middleware and https://redux.js.org/tutorials/fundamentals/part-6-async-logic#using-the-redux-thunk-middleware for examples.`
)
}
function isPlainObject(obj: any): boolean {
if (typeof obj !== 'object' || obj === null) return false
let proto = obj
while (Object.getPrototypeOf(proto) !== null) {
proto = Object.getPrototypeOf(proto)
}
return Object.getPrototypeOf(obj) === proto
}
2，没有type属性，报错。
所以，Action必须要有type属性。
if (typeof action.type === 'undefined') {
throw new Error(
'Actions may not have an undefined "type" property. You may have misspelled an action type string constant.'
)
}
3，正在执行中，报错。
if (isDispatching) {
throw new Error('Reducers may not dispatch actions.')
}
4，调用Reducer。
打开标记。
调用reducer，传入前状态，action。
返回新状态。
完毕后关闭标记。
try {
isDispatching = true
currentState = currentReducer(currentState, action)
} finally {
isDispatching = false
}
5，通知所有粉丝。
从next中拿current，再查询。
遍历，调用。
所以，订阅的基本单位是Store。
const listeners = (currentListeners = nextListeners)
for (let i = 0; i < listeners.length; i++) {
const listener = listeners[i]
listener()
}
6，返回该action
链式操作。
return action