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function thousand(num) {
  var num = num.toString();
  var reg = num.indexOf('.') > -1 ? /(\d)(?=(\d{3})+\.)/g : /(\d)(?=(\d{3})+\b)/g;
  return num.replace(reg, function($0, $1) {
    return $1 + ','
  })
}

thousand(231231)  // "231,231"

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/**
* 适用css3 transform进行动画，有的库会使用Object.defineProperty
*/
var requstAnimationFrame = (function() {
  var prefix = ['moz', 'ms', 'webkit', 'o'];
  var raf, caf;
  if (raf = window.requestAnimationFrame) {
    caf = window.cancelAnimationFrame;
  } else {
    for (var i = 0; i < prefix.length; i++) {

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// ES next中async/await proposal实现原理是什么？ - 何幻的回答 - 知乎
// https://www.zhihu.com/question/39571954/answer/82042148

// 实现依赖迭代器的await        配合js引擎的ast 解析* 和 yield
// 如果不懂promise实现原理，请看我的其他gist,有个实现promise的

function yieldPromise(generator) {
  var iterator = generator();
  recursiveCore.call(iterator);
}

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var nextTask = [];

var nextHandler;

function nextTick(fn, cxt = this, args = []) {
  nextTask.push(function() {
    return fn.apply(cxt, args);
  });
  if (nextHandler) {
    return;

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// 实现一个promise 拥有then方法

function noop() {
}

function resolve(promise) {
  return function(value) {
    if (promise._status !== 'pending') {
      return; // 如果是fullfilled或者rejected，不可逆
    }

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var util = {
    isType: function(value, type) {
        return Object.prototype.toString.call(value).toLowerCase().slice(8, -1) === type;
    }
};

function Iterator(list) {
  list = util.isType(list, 'array') ? list : [list];
  this._array = list;
  this._index = 0;

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//   实现以下功能
// function Animal(name, age) {
//   this.name = name;
//   this.age = age;
// }

// Animal.prototype.talk = function() {
//   return this.name + this.age;
// }

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// 可观察对象

function Observable(generator) {
  if (!(this instanceof Observable)) {
    throw Error('Observable must use new to construct');
  }
  this._generator = generator;
}

Observable.prototype.subscribe = function(observer) {

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async function a() {
  console.log('step into a');
  await b();
  console.log('will leave a');
}

async function b() {
  await c();

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// ** if 里面判断的是布尔值   在js里，只有'', null, undefined, 0, NaN五个值是false

if ([]) {
	console.log(1)
}  
// console.log(1)

if ({}) {
	console.log(1);
}