// 创建一个迭代器对象来访问数组
const iterableObj = { 
    names: ['1','2','3'], //[]可计算属性 
    [Symbol.iterator]:function (){ 
        let index = 0 
        return { 
          next: ()=>{ 
            if(index<this.names.length){ 
              return { 
                done:false,
                value:this.names[index++]
              } 
            }else{ 
              return { 
                done:true,
                value:undefined
              } 
            } 
         } 
      } 
   } 
} 
//iterableObj[Symbol.iterator] 就是一个可迭代对象
console.log(iterableObj[Symbol.iterator]) 
//调用iterableObj[Symbol.iterator]函数
const iterator = iterableObj[Symbol.iterator]() 
console.log(iterator.next())
console.log(iterator.next())
console.log(iterator.next())
console.log(iterator.next())
// {done: false, value: '1'}
// {done: false, value: '2'}
// {done: false, value: '3'}
// {done: true, value: undefined}
for (const item of iterableObj) {
  console.log(item)
}
// 1 2 3
// for of 可以遍历一个可迭代对象 
// for of 就是一个与语法糖，获取的是迭代器的next

// 案例: 创建一个教室类, 创建出来的对象都是可迭代对象
class Classroom {
  constructor(address, name, students) {
    this.address = address
    this.name = name
    this.students = students
  }
  entry(newStudent) {
    this.students.push(newStudent)
  }
  [Symbol.iterator]() {
    let index = 0
    return {
      next: () => {
        if (index < this.students.length) {
          return { done: false, value: this.students[index++] }
        } else {
          return { done: true, value: undefined }
        }
      },
      return: () => {
        console.log("迭代器提前终止了~")
        return { done: true, value: undefined }
      }
    }
  }
}
const classroom = new Classroom("3幢5楼205", "计算机教室", ["james", "kobe", "curry", "why"])
classroom.entry("lilei")
for (const stu of classroom) {
  console.log(stu)
  if (stu === "why") break
}
// kobe
// curry
// why
// 迭代器提前终止了~