迭代器模式

按顺序遍历对象内部元素

var getEach = function(arr, callback){
  for(let i = 0; i < arr.length; i++){
    callback(i, arr[i])
  }
}

getEach([1,2,3,4,5], function(key, value){
  console.log(key.value)
})

ES6的迭代器

内置了迭代器的：

Array, Map, set, String, arguments, NodeList

var arr = [1,2,3,]
// for(let i of arr){
//   console.log(i)
// }

// let if = arr[Symbol.iterator]()
// console.log(it.next())
// console.log(it.next())
// console.log(it.next())
// console.log(it.next())

var obj = {
  0: 0000,
  1: 1111,
  2: 2222,
  length: 3,
  [Symbol.iterator]:Array.prototype[Symbol.iterator]
}

for(let i of obj){
  console.log(i)
}