ES6 Iterator接口和for...of循环用法分析

<script>
// 数组已经帮我们内置这个Iterator接口
let arr = ['hello','world'];
let map = arr[Symbol.iterator](); // 数组直接调用iterator接口，返回一个对象map
console.log(map.next()); // {value: "hello", done: false} done:循环没有下一步状态：true没有，false:有状态，循环并没有结束
console.log(map.next()); // {value: "world", done: false}
console.log(map.next()); // {value: undefined, done: true}
</script>

<script>
let obj ={
  start: [1,5,7],
  end:[8,4,3],
  [Symbol.iterator](){
   let self = this;
   let index = 0;
   let arr = self.start.concat(self.end);
   let len = arr.length;
   return {
    next(){
     if(index<len){
      return{
       value:arr[index++],
       done:false
      }
     }else{
      return {
       value:arr[index++],
       done:true
      }
     }
    }
   }
  }
}
for(let key of obj){ // for...of 背后用的就是iterator接口
  console.log(key); // 1 5 7 8 4 3
}
</script>

<script>
let arr = ['xixiaoxian','jamin'];
for(let value of arr){
  console.log(value); // xixiaoxian  jamin
}
</script>