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JavaScript代码简洁之道

JavaScript代码简洁之道

原文链接:mmdjj

1.通过条件判断给变量赋值布尔值的正确姿势

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

// good
b = a === 'a'
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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
}
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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
}
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3.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
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4.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
}
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巧用数组方法,尽量避免用for循环

5.使用some方法判断是否满足条件的元素

// 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)
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6.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
})
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7.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]
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8.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]
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巧用对象方法,避免使用for...in

9.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]
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10.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']
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巧用解构简化代码

11.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]
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12.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 
}
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13.解构时重命名简化命名

有时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
}
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14.修改数组对象key

let arr = [
    {
        mingzi:'小明',
        nianling:23
    },
    {
        mingzi:'小明',
        nianling:23
    },
    {
        mingzi:'小明',
        nianling:23
    },
    {
        mingzi:'小明',
        nianling:23
    },
    {
        mingzi:'小明',
        nianling:23
    },
]

 function changeSelectKey(keyMap,query){
    let newArr = query;
    newArr.map((item, index)=>{
        let obj = newArr[index];
        for(let key in obj){
            let newkey = keyMap[key];
            if(newkey){
                obj[newkey] = obj[key];
                delete obj[key];
            }
        }
    })
    return newArr;
}

let keyMap = {
    mingzi:'name',
    nianling:'age'
}

changeSelectKey(keyMap, arr)
console.log(arr)
// [{name: "小明", age: 23},{name: "小明", age: 23},{name: "小明", age: 23},{name: "小明", age: 23}]

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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 
}
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16.||短路符设置默认值

let person = {
    name: '张三',
    age: 38
}

let name = person.name || '佚名'
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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
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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`)
}
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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)
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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)
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