1、通过条件判断给变量赋值布尔值的正确姿势

// bad

if (a === 'a') {

    b = true

} else {

    b = false

}




// good

b = a === 'a'

2、在if中判断数组长度不为零的正确姿势

// bad

if (arr.length !== 0) {

    // todo

}




// good

if (arr.length) {

    // todo

}

3、同理，在if中判断数组长度为零的正确姿势

// bad

if (arr.length === 0) {

    // todo

}




// good

if (!arr.length) {

    // todo

}

4、简单的if判断使用三元表达式

// bad

if (a === 'a') {

    b = a

} else {

    b = c

}




// good

b = a === 'a' ? a : c

5、使用includes简化if判断

// bad

if (a === 1 || a === 2 || a === 3 || a === 4) {

    // todo

}




// good

let arr = [1, 2, 3, 4]

if (arr.includes(a)) {

    // todo

}

巧用数组方法，尽量避免用for循环

6、使用some方法判断是否有满足条件的元素

// bad

let arr = [1, 3, 5, 7]

function isHasNum (n) {

    for (let i = 0; i < arr.length; i ++) {

        if (arr[i] === n) {

            return true

        }

    }

    return false

}




// good

let arr = [1, 3, 5, 7]

let isHasNum = n => arr.some(num => num === n)




// best

let arr = [1, 3, 5, 7]

let isHasNum = (n, arr) => arr.some(num => num === n)

7、使用forEach方法遍历数组，不形成新数组

// bad

for (let i = 0; i < arr.length; i ++) {

    // todo

    arr[i].key = balabala

}




// good

arr.forEach(item => {

    // todo

    item.key = balabala

})

8、使用filter方法过滤原数组，形成新数组

// bad

let arr = [1, 3, 5, 7],

    newArr = []

for (let i = 0; i < arr.length; i ++) {

    if (arr[i] > 4) {

        newArr.push(arr[i])

    }

}




// good

let arr = [1, 3, 5, 7]

let newArr = arr.filter(n => n > 4) // [5, 7]

9、使用map对数组中所有元素批量处理，形成新数组

// bad

let arr = [1, 3, 5, 7],   

    newArr = []

for (let i = 0; i < arr.length; i ++) {   

    newArr.push(arr[i] + 1)

}




// good

let arr = [1, 3, 5, 7]

let newArr = arr.map(n => n + 1) // [2, 4, 6, 8]

巧用对象方法，避免使用for...in

10、使用Object.values快速获取对象键值

let obj = {  

    a: 1,  

    b: 2

}

// bad

let values = []

for (key in obj) {  

    values.push(obj[key])

}




// good

let values = Object.values(obj) // [1, 2]

11、使用Object.keys快速获取对象键名

let obj = {   

    a: 1,   

    b: 2

}

// bad

let keys = []

for (value in obj) {  

    keys.push(value)

}




// good

let keys = Object.keys(obj) // ['a', 'b']

巧用解构简化代码

12、解构数组进行变量值的替换

// bad

let a = 1,  

    b = 2

let temp = a

a = b

b = temp




// good

let a = 1,  

    b = 2

[b, a] = [a, b]

13、解构对象

// bad

setForm (person) {  

    this.name = person.name   

    this.age = person.age

}




// good

setForm ({name, age}) {  

    this.name = name  

    this.age = age 

}

14、解构时重命名简化命名

有的后端返回的键名特别长，你可以这样干

// bad

setForm (data) {   

    this.one = data.aaa_bbb_ccc_ddd   

    this.two = data.eee_fff_ggg

}

// good

setForm ({aaa_bbb_ccc_ddd, eee_fff_ggg}) {  

    this.one = aaa_bbb_ccc_ddd  

    this.two = eee_fff_ggg

}




// best

setForm ({aaa_bbb_ccc_ddd: one, eee_fff_ggg: two}) {  

    this.one = one   

    this.two = two

}

15、解构时设置默认值

// bad

setForm ({name, age}) {  

    if (!age) age = 16   

    this.name = name  

    this.age = age 

}




// good

setForm ({name, age = 16}) {  

    this.name = name   

    this.age = age

}

16、||短路符设置默认值

let person = {   

    name: '张三',  

    age: 38

}




let name = person.name || '佚名'

17、&&短路符判断依赖的键是否存在防止报错'xxx of undfined'

let person = {   

    name: '张三',  

    age: 38,  

    children: {     

        name: '张小三'  

    }

}




let childrenName = person.children && person.childre.name

18、字符串拼接使用${}

let person = {  

    name: 'LiMing',   

    age: 18

}

// bad

function sayHi (obj) {  

    console.log('大家好，我叫' + person.name = '，我今年' + person.age + '了')

}




// good

function sayHi (person) {  

    console.log(`大家好，我叫${person.name}，我今年${person.age}了`)

}




// best

function sayHi ({name, age}) {   

    console.log(`大家好，我叫${name}，我今年${age}了`)

}

19、函数使用箭头函数

let arr [18, 19, 20, 21, 22]

// bad

function findStudentByAge (arr, age) {  

    return arr.filter(function (num) {    

        return num === age   

    })

}




// good

let findStudentByAge = (arr, age)=> arr.filter(num => num === age)

20、函数参数校验

// bad

let findStudentByAge = (arr, age) => {

    if (!age) throw new Error('参数不能为空')

    return arr.filter(num => num === age)

}




// good

let checkoutType = () => {

    throw new Error('参数不能为空')

}

let findStudentByAge = (arr, age = checkoutType()) =>

    arr.filter(num => num === age)