javascript设计模式之迭代器模式

//实现一个jq的$.each()迭代器

var arr = [1, 2, 3, 4, 5, 6, 7, 8]

var each = function(arr, callback){
  for(var i=0; i<arr.length; i++){
    callback.call(null, i, arr[i])  //把下标和元素当作参数传递给callback参数
  }
}

each(arr, function(i, n){
  console.log(i, n);
})

//类似于jquery的 $.each(arr, function(i,n){})

//对两个数组做相等性判断时，如果不改迭代器内部方法实现，只能通过each的回调函数进行实现，虽然能实现，但不是很优雅。
let compare = function (ary1, ary2) {
  if(ary1.length !== ary2.length){
    throw new Error('ar1和ary2长度不相等。')
  }

  each(ary1, function (i, n) {
    if(n !== ary2[i] ){
      throw new Error('ary1和ary2不相等。')
    }
  })

  console.log('ary1和ary2相等!');
}

compare([1,2,3], [1,2, 3])

let Iterator = function (obj) {
  let current = 0;

  let next = function () {
    current += 1
  }

  let isNotDone = function () {
    return current <= obj.length
  }

  let getCurrentItem = function () {
    return obj[current];
  }

  return {
    next,
    isNotDone,
    getCurrentItem
  }
}

//外部迭代器通过next方法进行手工迭代
let arr = ['a', true, false, '10', 88, 741]
let iterator1 = Iterator(arr)
console.log(iterator1.getCurrentItem()); // a
iterator1.next() 
console.log(iterator1.getCurrentItem()); // true
iterator1.next() 
console.log(iterator1.getCurrentItem()); // false
iterator1.next() 
console.log(iterator1.getCurrentItem()); // '10'


//改写compare函数
let compare = function (iterator1, iterator2) {
  while(iterator1.isNotDone() && iterator2.isNotDone()){
    if(iterator1.getCurrentItem() !== iterator2.getCurrentItem()){
      throw new Error('iterator1和iterator2不相等。')
    }
    iterator1.next()
    iterator2.next()
  }

  console.log('iterator1和iterator2相等。');
}

let iterator1 = Iterator([1, 2, 3, 4])
let iterator2 = Iterator([1, 2, 3, 4, 5])

compare(iterator1, iterator2)  //iterator1和iterator2不相等。

let Iterator = function (array) {
  let nextIndex = 0;

  return {
    next: function () {
      return nextIndex < array.length ?
          {value: array[nextIndex++], done: false}:
          {done: true};
    }
  }
}

let it = Iterator(['a', 3, 10])
console.log(it.next().value);  //a
console.log(it.next().value);  //3
console.log(it.next().value);  //10  迭代到这步已经把所有值都迭代完成
console.log(it.next().done);  //true