迭代器，其实就是根据index下标增加来实现的

  1. class MyIterator {
  2.   private container: Container;
  3.   private list: Array<any>;
  4.   private index: number;
  5.   constructor(container: Container) {
  6.     this.list = container.list
  7.     this.index = 0;
  8.   }
  10.   next() {
  11.     if (this.hasNext()) {
  12.       return this.list[this.index++]
  13.     }
  14.     return null
  15.   }
  17.   hasNext() {
  18.     if (this.index >= this.list.length) {
  19.       return false
  20.     }
  21.     return true
  22.   }
  23. }
  25. class Container {
  26.   list: Array<any>
  27.   constructor(list: Array<any>) {
  28.     this.list = list
  29.   }
  30.   getIterator() {
  31.     return new MyIterator(this)
  32.   }
  33. }
  35. const container = new Container([1, 2, 3, 4])
  36. const iterator = container.getIterator()
  37. console.log(iterator.next()) // 1
  38. console.log(iterator.next()) // 2
  39. console.log(iterator.next()) // 3
  40. console.log(iterator.next()) // 4
  41. console.log(iterator.next()) // null