JavaScript：if-else 的替代方法

if-else:

if (a == 1) {
     
   console.log('a1')
} else if (a == 2) {
     
   console.log('b2')
} else if (a == 3) {
     
   console.log('c3')
} else if (a == 4) {
     
   console.log('d4')
}

switch-case:

switch(a){
     
   case 1:
       console.log('a1');
       break;
   // ……
   case 4:
       console.log('d4');
       break;
}

object 映射:

定义一个 object 作为配置对象来存放不同状态，通过链表查找。

const statusMap = {
     
   1:()=>{
     
       console.log('a1')
   },
   2:()=>{
     
       console.log('b2')
   }
   // ……
}
// 执行
let a = 1
statusMap[a || 1]()

数组映射:

// 它就是个function，内容很复杂
const statusArr = [function(){
     
   console.log(1)
},
   function () {
     
       console.log(2)
   },]
let a = 1
statusArr[a || 1]()

不同 key 相同 value:

function f1 (){
     
   console.log(1)
}
function f2 (){
     
   console.log(2)
}
const statusMap={
     
   1:f1,
   2:f1,
   3:f1,
   4:f1,
   40:f2
}
let a = 2
statusMap[a]()

重构：

const statusMap = {
     
   '1,2,3,4,5': f1,
   40: f2
}
const keys = Object.keys(statusMap),
   len = keys.length
const getVal=(param='')=>{
     
   for (let i = 0; i < len; i++) {
     
       const key = keys[i],
           val = statusMap[key]
       if (key.includes(param)) {
     
           return val
       }
   }
}
let a = 2,
   handle = getVal(a)
handle()

map:

const map1 = new Map()
const statusArr = [1,2,3,4,5]
map1.set(statusArr,f1)

let handle = function(){
     }
const getVal = (param = '') => {
     
	for (let value of map1.entries()) {
     
   		console.log(JSON.stringify(value))
   		if (value[0].includes(param)){
     
       		console.log(value)
       		handle = value[1]
   		}
	}
}
const a = 2
getVal(a)
handle()

双数组:

const keyArr = ['1,2,3,4,5','40']
const valArr = [f1,f2]
const getVal = (param = '')=>{
     
   let index = keyArr.findIndex((it)=>{
     
       return it.includes(param)
   })
   return valArr[index]
}
let a = 2,
   handle = getVal(a)
handle()

利用数组提供的下标，将 key 和 value 对应起来，进而获取想要的值。

推荐链接：https://blog.csdn.net/qq_40259641/article/details/83866457