消除switch語句以獲得更好的代碼結構

• 代碼演化1：純switch

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

• 用三元運算符代替

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

• 更換action.type ===，用對象本身的方法

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

• 柯里化

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

• 增加是否為函數檢測

const action = {type: 'INCREMENT'}const executeIfFunction = f =>f instanceof Function ? f() : fconst switchcase = cases => defaultCase => key =>cases.hasOwnProperty(key) ? cases[key] : defaultCaseconst 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))

• switch應用--星期天轉換

const switchcase = cases => defaultCase => key =>cases.hasOwnProperty(key) ? cases[key] : defaultCaseconst 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()

參考鏈接---消除switch獲得更好的代碼結構（英文文檔-需翻墻）

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