var colors = ["red", "green", "blue"];
for(var i=0; i<colors.length; i++){
  console.log(colors[i]);
}

function createIterator(items) {
  var i = 0;
  
  return { // 返回一个迭代器对象
    next: function() { // 迭代器对象一定有个next()方法
      var done = (i >= items.length);
      var value = !done ? items[i++] : undefined;
      
      return { // next()方法返回结果对象
        value: value,
        done: done
      };
    }
  };
}

var iterator = createIterator([1, 2, 3]);

console.log(iterator.next()); // "{ value: 1, done: false}"
console.log(iterator.next()); // "{ value: 2, done: false}"
console.log(iterator.next()); // "{ value: 3, done: false}"
console.log(iterator.next()); // "{ value: undefiend, done: true}"
// 之后所有的调用都会返回相同内容
console.log(iterator.next()); // "{ value: undefiend, done: true}"

var colors = ["red", "green", "blue"];
var iterator = createIterator(colors);
while(!iterator.next().done){
  console.log(iterator.next().value);
}

function *createIterator(items) {
  for(let i=0; i<items.length; i++) {
    yield items[i];
  }
}

let iterator = createIterator([1, 2, 3]);

// 既然生成器返回的是迭代器，自然就可以调用迭代器的next()方法
console.log(iterator.next()); // "{ value: 1, done: false}"
console.log(iterator.next()); // "{ value: 2, done: false}"
console.log(iterator.next()); // "{ value: 3, done: false}"
console.log(iterator.next()); // "{ value: undefiend, done: true}"
// 之后所有的调用都会返回相同内容
console.log(iterator.next()); // "{ value: undefiend, done: true}"

function *createIterator(items) { ... }

let createIterator = function *(item) { ... }

let o = {
  createIterator: function *(items) { ... }
};

let iterator = o.createIterator([1, 2, 3]);

let o = {
  *createIterator(items) { ... }
};

let iterator = o.createIterator([1, 2, 3]);

var colors = ["red", "green", "blue"];
for(let color of colors){
  console.log(color);
}

let values = [1, 2, 3];
let iterator = values[Symbol.iterator]();

console.log(iterator.next()); // "{ value: 1, done: false}"
console.log(iterator.next()); // "{ value: 2, done: false}"
console.log(iterator.next()); // "{ value: 3, done: false}"
console.log(iterator.next()); // "{ value: undefined, done: true}"

function isIterator(object) {
  return typeof object[Symbol.iterator] === "function";
}

console.log(isIterable([1, 2, 3])); // true
console.log(isIterable(new Set())); // true
console.log(isIterable(new Map())); // true
console.log(isIterable("Hello")); // true

let collection = {
  items: [],
  *[Symbol.iterator]() { // 将生成器赋值给对象的Symbol.iterator属性来创建默认的迭代器
    for(let item of this.items) {
      yield item;
    }
  }
};

collection.items.push(1);
collection.items.push(2);
collection.items.push(3);

for(let x of collection) {
  console.log(x);
}

let colors = [ "red", "green", "blue"];
let tracking = new Set([1234, 5678, 9012]);
let data = new Map();

data.set("title", "Understanding ECMAScript 6");
data.set("format", "print");

// 与调用colors.values()方法相同
for(let value of colors) {
  console.log(value);
}

// 与调用tracking.values()方法相同
for(let num of tracking) {
  console.log(num);
}

// 与调用data.entries()方法相同
for(let entry of data) {
  console.log(entry);
}

for(let [key, value] of data) {
  console.log(key + "=" + value);
}

let set = new Set([1, 2, 3, 4, 5]),
  array = [...set];
  
console.log(array); // [1,2,3,4,5]