javascript – 什么是双箭头功能？

什么是“让x = something1 => something2 => something3”？

我有这个代码,我无法理解它做了什么.

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;
  }, {});
};

您需要的完整代码：

//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);

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

解决方法:

让x = something1 => something2 => something3几乎与以下内容相同：

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

唯一的区别是,箭头具有这种词法绑定,即在编译时绑定.

标签：javascript,typescript,arrow-functions
来源： https://codeday.me/bug/20190608/1199613.html