什麼是雙箭頭功能？

Question

什麼是「let x = something1 => something2 => something3」？

我有這段代碼，我不明白它做了什麼。

const myReducers = {person, hoursWorked}; 
const combineReducers = reducers => (state = {}, action) => { 
    return Object.keys(reducers).reduce((nextState, key) => { 
    nextState[key] = reducers[key](state[key], action); 
    return nextState; 
    }, {}); 
}; 

完整的代碼櫃面你需要：

//Redux-Style Reducer 
const person = (state = {}, action) => { 
    switch(action.type){ 
    case 'ADD_INFO': 
     return Object.assign({}, state, action.payload) 
    default: 
     return state; 
    } 
} 

const infoAction = {type: 'ADD_INFO', payload: {name: 'Brian', framework: 'Angular'}} 
const anotherPersonInfo = person(undefined, infoAction); 
console.log('***REDUX STYLE PERSON***: ', anotherPersonInfo); 

//Add another reducer 
const hoursWorked = (state = 0, action) => { 
    switch(action.type){ 
    case 'ADD_HOUR': 
     return state + 1; 
    case 'SUBTRACT_HOUR': 
     return state - 1; 
    default: 
     return state; 
    } 
} 
//Combine Reducers Refresher 

****HERE**** 
****HERE**** 
****HERE**** 

const myReducers = {person, hoursWorked}; 
const combineReducers = reducers => (state = {}, action) => { 
    return Object.keys(reducers).reduce((nextState, key) => { 
    nextState[key] = reducers[key](state[key], action); 
    return nextState; 
    }, {}); 
}; 


**** 
**** 


/* 
This gets us most of the way there, but really want we want is for the value of firstState and secondState to accumulate 
as actions are dispatched over time. Luckily, RxJS offers the perfect operator for this scenario., to be discussed in next lesson. 
*/ 
const rootReducer = combineReducers(myReducers); 
const firstState = rootReducer(undefined, {type: 'ADD_INFO', payload: {name: 'Brian'}}); 
const secondState = rootReducer({hoursWorked: 10, person: {name: 'Joe'}}, {type: 'ADD_HOUR'}); 
console.log('***FIRST STATE***:', firstState); 
console.log('***SECOND STATE***:', secondState); 

來源：https://gist.github.com/btroncone/a6e4347326749f938510

Answer 1

設X = something1 => something2 => something3是如下面的幾乎相同：

let x = function (something) { 
 
    return function (something2) { 
 
    return something3 
 
    } 
 
}

唯一的區別是，箭頭具有this詞法結合，即，在編譯結合時間。

Answer 2

箭頭功能

someParameters => someExpression 

那麼，什麼是

someParameters => someThing => someThingElse 

???

好，通過簡單的傻瓜 「模式匹配」，這是一個箭頭的功能，它的機身（someExpression）是

someThing => someThingElse 

換句話說，它是

someParameters => someOtherParameters => someExpression 

沒有什麼特別之處。函數是對象，它們可以從函數返回，而不管這些函數是使用箭頭還是關鍵字function寫入的。

你真的需要知道讀這正確的是，箭頭是右結合的唯一的事情，督察該

a => b => c === a => (b => c) 

---

注：箭頭的功能也可以由語句的身體以及一個單一的表達。我具體指的是OP令人困惑的形式。