<script>
// 數組已經幫我們內置這個Iterator接口
let arr = ['hello','world'];
let map = arr[Symbol.iterator](); // 數組直接調用iterator接口，返回一個對象map
console.log(map.next()); // {value: "hello", done: false} done:循環沒有下一步狀態：true沒有，false:有狀態，循環并沒有結束
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>