es6(14)--iterator for ...of循环

 //iterator  for ...of循环
 {
     let arr=['hello','world'];
     let map=arr[Symbol.iterator]();
     console.log(map.next())
     console.log(map.next())
     console.log(map.next())
 }
 {
     let obj={
         start:[1,3,2],
         end:[7,9,8],
         [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){
         console.log(key)
     }
 }
 {
     let arr=['hello','world'];
     for(let value of arr){
         console.log('value',value)
     }
 }