20條JavaScript代碼簡潔的寫法

1、通過條件判斷給變量指派布爾值的正确姿勢

// bad
if (a === 'a') {
    b = true
} else {
    b = false
}


// good
b = a === 'a'      

2、在if中判斷數組長度不為零的正确姿勢

// bad
if (arr.length !== 0) {
    // todo
}


// good
if (arr.length) {
    // todo
}      

3、同理，在if中判斷數組長度為零的正确姿勢

// bad
if (arr.length === 0) {
    // todo
}


// good
if (!arr.length) {
    // todo
}      

4、簡單的if判斷使用三元表達式

// bad
if (a === 'a') {
    b = a
} else {
    b = c
}


// good
b = a === 'a' ? a : c      

5、使用includes簡化if判斷

// bad
if (a === 1 || a === 2 || a === 3 || a === 4) {
    // todo
}


// good
let arr = [1, 2, 3, 4]
if (arr.includes(a)) {
    // todo
}      

巧用數組方法，盡量避免用for循環

6、使用some方法判斷是否有滿足條件的元素

// 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方法周遊數組，不形成新數組

// 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方法過濾原數組，形成新數組

// 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對數組中所有元素批量處理，形成新數組

// 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]      

巧用對象方法，避免使用for...in

10、使用Object.values快速擷取對象鍵值

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快速擷取對象鍵名

let obj = {   
    a: 1,   
    b: 2
}
// bad
let keys = []
for (value in obj) {  
    keys.push(value)
}


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

巧用解構簡化代碼

12、解構數組進行變量值的替換

// bad
let a = 1,  
    b = 2
let temp = a
a = b
b = temp


// good
let a = 1,  
    b = 2
[b, a] = [a, b]      

13、解構對象

// bad
setForm (person) {  
    this.name = person.name   
    this.age = person.age
}


// good
setForm ({name, age}) {  
    this.name = name  
    this.age = age 
}      

14、解構時重命名簡化命名

有的後端傳回的鍵名特别長，你可以這樣幹

// 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、解構時設定預設值

// 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、||短路符設定預設值

let person = {   
    name: '張三',  
    age: 38
}


let name = person.name || '佚名'      

17、&&短路符判斷依賴的鍵是否存在防止報錯'xxx of undfined'

let person = {   
    name: '張三',  
    age: 38,  
    children: {     
        name: '張小三'  
    }
}


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

18、字元串拼接使用${}

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、函數使用箭頭函數

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、函數參數校驗

// bad
let findStudentByAge = (arr, age) => {
    if (!age) throw new Error('參數不能為空')
    return arr.filter(num => num === age)
}


// good
let checkoutType = () => {
    throw new Error('參數不能為空')
}
let findStudentByAge = (arr, age = checkoutType()) =>
    arr.filter(num => num === age)      

本文完~