修饰器是一个函数，用来修改类的行为(扩展类的功能)

{
  let readonly = function (target, name, descriptor) {
    descriptor.writable = false
    return descriptor
  }

  class Test {
    @readonly
    time() {
      return '2020-04-06'
    }
  }

  let test = new Test()

  // test.time = function () {
  //   console.log("reset time");
  // };

  console.log(test.time()) // 2020-04-06
}

{
  let typename = function (target, name, descriptor) {
    target.myname = 'hello'
  }

  @typename
  class Test {}

  console.log('类修饰符', Test.myname) // 类修饰符 hello
  // 第三方库修饰器的js库：core-decorators; npm install core-decorators
}

{
  // 实现埋点业务逻辑拆分
  // 埋点接口 逻辑
  let log = (type) => {
    return function (target, name, descriptor) {
      let src_method = descriptor.value
      descriptor.value = (...arg) => {
        src_method.apply(target, arg)
        console.info(`log ${type}`)
      }
    }
  }

  // 广告方法逻辑
  class AD {
    @log('show')
    show() {
      console.info('ad is show')
    }
    @log('click')
    click() {
      console.info('ad is click')
    }
  }

  let ad = new AD()
  ad.show()
  // ad is show
  // log show
  ad.click()
  // ad is click
  // log cick
}