1. 实例演示class类与extends,super等的用法 2. 实例演示字符串,数组常用API

1. 实例演示class类与extends,super等的用法

2. 类声明

   let User = class {
   构造函数:声明属性
   constructor(uname, email) {
   (1) 属性
    this.uname = uname
    this.email = email
   }
   (2) 方法
   say() {
    return `${this.uname}: ( ${this.email} )`
   }
   (3) 静态成员
   static nation = 'CHINA'
   }

3. 类的实例化

const user = new User('王小二', 'wang@qq.com')
console.log(user.say())
console.log(User.nation)
 继承
class Child extends User {
  constructor(uname, email, sex) {
  // super 调用父类成员
    super(uname, email)
  // 子类扩展的属性
    this.sex = sex
  }
  say() {
    // super.say() 父类中的say()
    return `${super.say()}, (${this.sex})`
  }
}
const child = new Child('仙女', 'xn@qq.com', '女')
console.log(child.say())
 ! 在类中使用"访问器属性"
const Stu = class {
  #age = 18
  get age() {
    return this.#age
  }
  set age(age) {
    if (age >= 18 && age <= 100) {
      this.#age = age
    } else {
      console.log('年龄必须在18-100之间')
    }
  }
}
let stu = new Stu()
console.log('age = ', stu.age)
// stu.age = 120
stu.age = 30
console.log('age = ', stu.age)

1. 实例演示字符串,数组常用API
   数组 API -1
   包括对象在内, 尽量只用字面量来声明

   let arr = [1, 2, 'a', 'b', true, { x: 1, y: 2 }, [1, 2, 3], function () {}]
   console.log(arr)

   …rest 压缩与展开

   arr = [1, 2, 3]
   let arr1 = [...arr]
   console.log(arr1)
   arr = [...arr, 4, 5, 6]
   console.log(arr)
   console.log('--------------------')

   Array.of 打包

   let items = [1, 2, 3, 4, 5, 6]
   console.log(Array.of(...items))

   Array.from(): 类数组(对象) -> 包装成一个真正的数组

   const likeArr = {
   0: 'red',
   1: 'blue',
   2: 'green',
   length: 3,
   }

   为什么要转为真数组?
   因为数组上有非常多的方法可以使用

const data = Array.from(likeArr)
console.log(Array.isArray(data) ? 'Array' : 'No Array')
for (let item of data) {
  console.log(item)
}