20条JavaScript代码简洁的写法

　　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 : c5、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.name18、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)