对象和Iterator

对象想要被遍历

要做些改变

添加一个Symbol.iterator的属性。

 1 class RangeIterator {
 2   constructor(start, stop) {
 3     this.value = start;
 4     this.stop = stop;
 5   }
 6 
 7   [Symbol.iterator]() { return this; }
 8 
 9   next() {
10     var value = this.value;
11     if (value < this.stop) {
12       this.value++;
13       return {done: false, value: value};
14     }
15     return {done: true, value: undefined};
16   }
17 }
18 
19 function range(start, stop) {
20   return new RangeIterator(start, stop);
21 }
22 
23 for (var value of range(0, 3)) {
24   console.log(value); // 0, 1, 2
25 }