ES6新特性二：Iterator(遍历器)和for-of循环详解

var arr = [1,2,3,4,5,6];
arr.name = 'a';
for (var index = 0; index < arr.length; index++) {
  console.log(arr[index]);
}
arr.forEach(function (value) { //ES5 内建的forEach方法 缺陷：无法使用break 中断 ，也不能使用return 语句返回到外层函数
  console.log(value);
});

for (var index in arr) { // 千万别这样做
 console.log(arr[index]);
}

var b = 0;
for (var index in arr) {
 b = b+ index;
 console.log(b)
}

for(var value of arr){
  console.log(value)
}

var words = 'a';
var s = new Set();
s.add("a");
s.add(1);
for(var word of s){
  console.log(word);
}

var map = new Map();
map.set('a',1);
map.set('b',2);
map.set('c',3);
map.set('d',4);
for(var [key,value] of map){
  console.log(key+':'+value);
}

//模拟遍历器原理
function makeIterator(array){
  var nextIndex = 0;
  return {
    next: function(){
      return nextIndex < array.length ?
        {value: array[nextIndex++], done: false} :
        {value: undefined, done: true};
    }
  }
}
var it = makeIterator(['a', 'b']);
console.log(it.next());//{ value: 'a', done: false }
console.log(it.next());//{ value: 'b', done: false }
console.log(it.next());//{ value: undefined, done: true }

var map = new Map();
console.log(map[Symbol.iterator] === map.entries)//true
var arr = new Array();
console.log(arr[Symbol.iterator] === arr.values)//true
var set = new Set();
console.log(set[Symbol.iterator] === set.values)//true

var students = {}
students[Symbol.iterator] = function() {
 let index = 1;
 return {
  next() {
   return {done: index>10, value: index++}
  }
 }
}
for(var i of students) {
 console.log(i);
}//