js闭包/类创建/解构赋值

闭包(1.父子函数 2.子函数调用了父函数中的变量)

function f2(){
  let a = 1;
  return function (){
    retrun (a = a + 1);
  }
}
const f = f2();
console.log(f());//1
console.log(f());//2

• 闭包:偏函数

//分批传入参数
fn = function(a){
  return function(b){
    return function(c){
      return a + b + c;
    }
  }
}
//箭头函数简写
fn = a => b => c => a+b+c;
console.log(fn(1)(2)(3));
//或者
f = fn(1);
f2 = fn(2);
console.log(f2(3));

• 把闭包:纯函数

let discound = 0.8;
function getPrice(price, discound = 1) {
  // 纯函数中禁用有自由变量
  return price * discound;
}
console.log(getPrice(12000, discound));

访问器属性

let user = {
  data:{name:"nn",email:"email"},
  // 访问email [注意空格必须]
  get email(){
    return user.data.email;  
  },
  // 设置email [注意空格必须]
  set email(email){
    this.data.email = email;
  }
};
user.email = "mm";
console.log(user.email)

类与构造函数

• js老方法实现

//首字母必须大写
let User = function(name,email,sex){
  //私有成员
  let gender = sex;
  this.name = name;
  this.email = email;
}
//调用
const user1 = new User("admin","email","male");
//给User添加方法
User.prototype.getInfo = function(){
  retrun `name = ${this.name},email = ${this.email}`;
}
console.log(user1.getInfo);
//静态成员直接挂载到对象上的属性
User.status = "enabled";
console.log(User.status);

• ES6 class实现

class User1{
  //公共字段(可选)
  name = 'username';
  email = 'email.com';
  //私有成员
  #gender = 'male';
  //构造方法
  constructor(name,enmail,sex){
    this.name = name;
    this.email = email;
    this.#gender = sex;
  }
  //公共方法:原型
  getInfo(){
    return `name = ${this.name},email = ${this.email}`;
  }
  //静态成员
  static status = "enabled";
}
//调用
const user4 = new User1("name","email","sex");
//继承
class Child extends User1{
  constructor(name,email,sex,salary){
    //调用父级构造函数
    super(name,email,sex);
    //子类新属性
    this.salary = salary;
  }
  //重写父类方法
  getInfo(){
    //调用父类方法
    return `${super.getInfo()},salary = ${this.salary}`;
  }
}
//调用
const user5 = new User1("name2","email2","sex2","123456");
//在类中使用访问器属性(访问与修改私有成员)
class Stu{
  #age = 0;
  get age(){
    return this.#age;
  }
  set age(age){
    this.age = age;
  }
}
//调用
let stu = new Stu();
//设置
stu.age = 100;
//访问
stu.age

解构赋值

• 数组解构

//age 默认值
let [name,email,age = 10] = ["nn","ee"];
console.log(name,email);

• 对象解构

//对象模板必须等于对象字面量
let {id,lesson,score} = {id:1,lesson:'js',score:80}
//再次赋值必须加括号包含
({id,lesson,score}) = {id:2,lesson:'js2',score:22}
//别名(命名冲突时使用)
let {id:userId,lesson:userLesson,score:userScore} = {id:2,lesson:'js2',score:22}
console.log(userId);
//克隆对象
let {...obj} = {id:1,lesson:'js',score:80}
//案例
function getUser({id,name,email}){
  //解构传参
  console.log(id,name,email);
}
getUser({id:123,name:'name','email'})