消除switch语句以获得更好的代码结构

• 代码演化1：纯switch

function counter(state = 0, action) {  switch (action.type) {    case 'INCREMENT':      return state + 1    case 'DECREMENT':      return state - 1    default:      return state  }}复制代码

• 用三元运算符代替

const counter = (state = 0, action) =>  action.type === 'INCREMENT'   ? state + 1  : action.type === 'DECREMENT' ? state - 1                                : state复制代码

• 更换action.type ===，用对象本身的方法

function switchcase (cases, defaultCase, key) {  if (cases.hasOwnProperty(key)) {    return cases[key]  } else {    return defaultCase  }}复制代码

• 柯里化

const switchcase = cases => defaultCase => key =>  cases.hasOwnProperty(key) ? cases[key] : defaultCase  const counter = (state = 0, action) =>  switchcase({    'INCREMENT': state + 1,    'DECREMENT': state -1  })(state)(action.type)复制代码

• 增加是否为函数检测

const action = {      type: 'INCREMENT'    }    const executeIfFunction = f =>      f instanceof Function ? f() : f    const switchcase = cases => defaultCase => key =>      cases.hasOwnProperty(key) ? cases[key] : defaultCase    const switchcaseF = cases => defaultCase => key =>      executeIfFunction(switchcase(cases)(defaultCase)(key))    const counter = (state = 0, action) =>      switchcaseF({        'INCREMENT': () => state + 1,        'DECREMENT': () => state - 1      })(state)(action.type)    console.log(counter(0, action))复制代码

• switch应用--星期天转换

const switchcase = cases => defaultCase => key =>      cases.hasOwnProperty(key) ? cases[key] : defaultCase       const getDay = switchcase({      0: 'Sunday',      1: 'Monday',      2: 'Tuesday',      3: 'Wednesday',      4: 'Thursday',      5: 'Friday',      6: 'Saturday'    })('Unknown')    const getCurrentDay = () => getDay(new Date().getDay())    const day = getCurrentDay()复制代码