ES6相关

// set 数据结构（类数组，无数值下标）
let setArr = new Set ()

// 添加值
setArr.add('a')
setArr.add('b')
setArr.add('c')

// 以上可以写成
let setArr = new Set ().add('a').add('b').add('c')

console.log(setArr)

// 删除值
setArr.delete('b')
console.log(setArr)

// 判断该值是否存在
console.log(setArr.has('a'))    // true
console.log(setArr.has('b'))    // false

// 输出元素个数
console.log(setArr.size)        // 2

// 清空元素
setArr.clear()

// 循环遍历数据
for(let item of setArr){
	console.log(item)
}  // a , c  默认遍历values

// 循环遍历数据
for(let item of setArr.values()){
	console.log(item)
}  // a , c

// 循环遍历下标
for(let item of setArr.keys()){
	console.log(item)
}  // a , c

// 循环遍历
for(let item of setArr.entries()){
	console.log(item)
}  // ["a", "a"] , ["c", "c"]

// 循环遍历
setArr.forEach((value,index) => {
   console.log(value,index)
})  // a a , c c

// 存放数组
let set = new Set()
let json = {
  a: 1,
  b: 2,
  c: 3
}
let json2 = {
  a: 1,
  b: 2,
  c: 3
}
set.add(json).add(json2)
set.forEach((item) => console.log(item))  // {a: 1, b: 2, c: 3} , {a: 1, b: 2, c: 3}

// 数组去重
let arr = [1, 2, 3, 4, 6, 7, 9, 8, 5, 4, 6, 7, 8, 4, 5, 6, 2]
let newArr = [...new Set(arr)]
console.log(newArr)      // [1, 2, 3, 4, 6, 7, 9, 8, 5]

// 映射新数组
let set = new Set([1, 2, 3, 4, 5])
set = new Set([...set].map(val => val * 2))
console.log(set)     // Set(5) {2, 4, 6, 8, 10}   

// 过滤
let set = new Set([1, 2, 3, 4, 5])
set = new Set([...set].filter(val => val % 2 == 0))
console.log(set)     // Set(2) {2, 4}

// 存放数组
let wSet = new WeakSet()
let json = {
  a: 1,
  b: 2,
  c: 3
}
let json2 = {
  a: 1,
  b: 2,
  c: 3
}
set.add(json).add(json2)
console.log(wSet)  // WeakSet {{…}, {…}}

// 新建Map
let map = new Map ()
let json = {
  name: 'zephyr',
  age: 22
}

// 设置值
map.set('a',"aaa")
map.set(json,"aaa")
map.set('aaa',json)

// 输出值
console.log(map)   // Map(3) {"a" => "aaa", {…} => "aaa", "aaa" => {…}}

// 删除值
map.delete('aaa')
// 获取值
console.log(map.get('aaa'))    // undefined

// 判断值
console.log(map.has('aaa'))    // false

// 清空Map
map.clear()
console.log(map)    // Map(0) {}

// for...of循环Map
for(let [k,v] of map){
  console.log(k,v)
}       // a aaa , {name: "zephyr", age: 22} "aaa" , aaa {name: "zephyr", age: 22}

// forEach循环Map
map.forEach((k,v) => console.log(k,v))   //aaa a , aaa {name: "zephyr", age: 22} , {name: "zephyr", age: 22} "aaa"

var wm1 = new WeakMap(),
    wm2 = new WeakMap(),
    wm3 = new WeakMap();
var o1 = {},
    o2 = function(){},
    o3 = window;

wm1.set(o1, 37);
wm1.set(o2, "azerty");
wm2.set(o1, o2); // value可以是任意值,包括一个对象
wm2.set(o3, undefined);
wm2.set(wm1, wm2); // 键和值可以是任意对象,甚至另外一个WeakMap对象
wm1.get(o2); // "azerty"
wm2.get(o2); // undefined,wm2中没有o2这个键
wm2.get(o3); // undefined,值就是undefined

wm1.has(o2); // true
wm2.has(o2); // false
wm2.has(o3); // true (即使值是undefined)

wm3.set(o1, 37);
wm3.get(o1); // 37
wm3.clear();
wm3.get(o1); // undefined,wm3已被清空
wm1.has(o1);   // true
wm1.delete(o1);
wm1.has(o1);   // false

// 二进制 （binary）
let a = 0b010101
console.log(a)   // 21

// 八进制 （octal）
let b = 0o666
console.log(b)   // 438

// 判断NaN
Number.isNaN(NaN) --> true

// 判断Number
Number.isFinite(1.5) --> true
Number.isFinite(true) --> false

// 判断整数
Number.isInteger(1) --> true
Number.isInteger(1.5) --> false

let a = 2 ** 53
console.log(Number.isSafeInteger(a))         // false
console.log(Number.isSafeInteger(a - 1))     // true

let a = 2 ** 53 - 1
console.log(a)                               // 9007199254740991
console.log(Number.MAX_SAFE_INTEGER)         // 9007199254740991

// 截取，只保留整数部分
Math.trunc(1.1)    // 1
Math.trunc(1.9)    // 1

// 判断正负
Math.sign(1)         // 1
Math.sign(1.5)       // 1
Math.sign(-1)        // -1
Math.sign(-1.5)      // -1
Math.sign(0)         // 0
Math.sign(-0)        // -0
Math.sign('aaa')     // NaN

// 计算立方根
Math.cbrt(27)        // 3

// 语法 （?<name>）
let str = '2019-03-30'
let reg = /(\d{4})-(\d{2})-(\d{2})/
console.log(str.match(reg))   // ["2019-03-30", "2019", "03", "30", index: 0, input: "2019-03-30", groups: undefined]

// 使用命名捕获
let str = '2019-03-30'
let reg = /(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/
let dateArr = str.match(reg).groups
console.log(dateArr)     // { year: "2019", month: "03", day: "30" }

let { year, month, day} = str.match(reg).groups
console.log(year, month, day)    // 2019 03 30

// 普通反向引用
\1  \2  $1  $2

// 反向引用命名捕获语法 （\<name>）
let reg = /^(?<zephyr>welcome)-\k<zephyr>$/
let str = 'a-a'
let str2 = 'zephyr-zephyr'
let str3 = 'welcome-welcome'
console.table(reg.test(str),reg.test(str3),reg.test(str3))    // false true true

new Proxy (target, handler)  // 被代理的对象，对代理对象进行的操作

// 实例
let obj = {
  name: 'zephyr'
}

console.log(obj.name)
let newObj = new Proxy(obj, {
  get(targrt, property) {
    // console.log(targrt, property)
    console.log(`你访问了${property}属性！`)
    return targrt[property]
  }
})

newObj.name   // zephyr , 你访问了name属性！

let obj = {
  name: 'zephyr'
}

console.log(obj.name)
let newObj = new Proxy(obj, {
  get(targrt, property) {
    return targrt[property]
  }
})

console.log(newObj.name)   // zephyr
console.log(newObj.age)    // undefined

// 自定义捕获错误并显示提示消息
let obj = {
  name: 'zephyr'
}
console.log(obj.name)

let newObj = new Proxy(obj, {
  get(targrt, property) {
    if (property in targrt) {
      return targrt[property]
    } else {
      throw new ReferenceError(`${property}属性不在此对象上！`)
    }
  }
})

newObj.name    // zephyr
newObj.age     // Uncaught ReferenceError: age属性不在此对象上！

const hide2 = (el) => Array.from(el).forEach(e => (e.style.display = 'none'));
// 事例:隐藏页面上所有`<img>`元素?
hide(document.querySelectorAll('img'))

const hasClass = (el, className) => el.classList.contains(className)
// 事例
hasClass(document.querySelector('p.special'), 'special') // true

const toggleClass = (el, className) => el.classList.toggle(className)
// 事例 移除 p 具有类`special`的 special 类
toggleClass(document.querySelector('p.special'), 'special')

const getScrollPosition = (el = window) => ({
  x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft,
  y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop
});
// 事例
getScrollPosition(); // {x: 0, y: 200}

const scrollToTop = () => {
  const c = document.documentElement.scrollTop || document.body.scrollTop;
  if (c > 0) {
    window.requestAnimationFrame(scrollToTop);
    window.scrollTo(0, c - c / 8);
  }
}
// 事例
scrollToTop()

const elementContains = (parent, child) => parent !== child && parent.contains(child);
// 事例
elementContains(document.querySelector('head'), document.querySelector('title')); 
// true
elementContains(document.querySelector('body'), document.querySelector('body')); 
// false

const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
  const { top, left, bottom, right } = el.getBoundingClientRect();
  const { innerHeight, innerWidth } = window;
  return partiallyVisible
    ? ((top > 0 && top < innerHeight) || (bottom > 0 && bottom < innerHeight)) &&
        ((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
    : top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
};
// 事例
elementIsVisibleInViewport(el); // 需要左右可见
elementIsVisibleInViewport(el, true); // 需要全屏(上下左右)可以见

const getImages = (el, includeDuplicates = false) => {
  const images = [...el.getElementsByTagName('img')].map(img => img.getAttribute('src'));
  return includeDuplicates ? images : [...new Set(images)];
};
// 事例：includeDuplicates 为 true 表示需要排除重复元素
getImages(document, true); // ['image1.jpg', 'image2.png', 'image1.png', '...']
getImages(document, false); // ['image1.jpg', 'image2.png', '...']

const detectDeviceType = () =>
  /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)
    ? 'Mobile'
    : 'Desktop';
// 事例
detectDeviceType(); // "Mobile" or "Desktop"

const currentURL = () => window.location.href
// 事例
currentURL() // 'https://google.com'

const getURLParameters = url =>
  (url.match(/([^?=&]+)(=([^&]*))/g) || []).reduce(
    (a, v) => ((a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1)), a),
    {}
  );
// 事例
getURLParameters('http://url.com/page?n=Adam&s=Smith'); // {n: 'Adam', s: 'Smith'}
getURLParameters('google.com'); // {}

const formToObject = form =>
  Array.from(new FormData(form)).reduce(
    (acc, [key, value]) => ({
      ...acc,
      [key]: value
    }),
    {}
  );
// 事例
formToObject(document.querySelector('#form')); 
// { email: 'test@email.com', name: 'Test Name' }

const get = (from, ...selectors) =>
  [...selectors].map(s =>
    s
      .replace(/\[([^\[\]]*)\]/g, '.$1.')
      .split('.')
      .filter(t => t !== '')
      .reduce((prev, cur) => prev && prev[cur], from)
  );
const obj = { selector: { to: { val: 'val to select' } }, target: [1, 2, { a: 'test' }] };
// Example
get(obj, 'selector.to.val', 'target[0]', 'target[2].a'); 
// ['val to select', 1, 'test']

const delay = (fn, wait, ...args) => setTimeout(fn, wait, ...args);
delay(
  function(text) {
    console.log(text);
  },
  1000,
  'later'
); 
// 1秒后打印 'later'

const triggerEvent = (el, eventType, detail) =>
  el.dispatchEvent(new CustomEvent(eventType, { detail }));
// 事例
triggerEvent(document.getElementById('myId'), 'click');
triggerEvent(document.getElementById('myId'), 'click', { username: 'bob' });

// 向 window派发一个resize内置事件
window.dispatchEvent(new Event('resize'))
 
// 直接自定义事件，使用 Event 构造函数：
var event = new Event('build');
var elem = document.querySelector('#id')
// 监听事件
elem.addEventListener('build', function (e) { ... }, false);
// 触发事件.
elem.dispatchEvent(event);

var myEvent = new CustomEvent(eventname, options);
其中 options 可以是：
{
  detail: {
    ...
  },
  bubbles: true,    //是否冒泡
  cancelable: false //是否取消默认事件
}

element.dispatchEvent(customEvent);

// add an appropriate event listener
obj.addEventListener("cat", function(e) { process(e.detail) });
 
// create and dispatch the event
var event = new CustomEvent("cat", {"detail":{"hazcheeseburger":true}});
obj.dispatchEvent(event);
使用自定义事件需要注意兼容性问题，而使用 jQuery 就简单多了：
// 绑定自定义事件
$(element).on('myCustomEvent', function(){});
 
// 触发事件
$(element).trigger('myCustomEvent');
// 此外，你还可以在触发自定义事件时传递更多参数信息：
 
$( "p" ).on( "myCustomEvent", function( event, myName ) {
  $( this ).text( myName + ", hi there!" );
});
$( "button" ).click(function () {
  $( "p" ).trigger( "myCustomEvent", [ "John" ] );
});

const off = (el, evt, fn, opts = false) => el.removeEventListener(evt, fn, opts);
const fn = () => console.log('!');
document.body.addEventListener('click', fn);
off(document.body, 'click', fn);

const formatDuration = ms => {
  if (ms < 0) ms = -ms;
  const time = {
    day: Math.floor(ms / 86400000),
    hour: Math.floor(ms / 3600000) % 24,
    minute: Math.floor(ms / 60000) % 60,
    second: Math.floor(ms / 1000) % 60,
    millisecond: Math.floor(ms) % 1000
  };
  return Object.entries(time)
    .filter(val => val[1] !== 0)
    .map(([key, val]) => `${val} ${key}${val !== 1 ? 's' : ''}`)
    .join(', ');
};
// 事例
formatDuration(1001); // '1 second, 1 millisecond'
formatDuration(34325055574); 
// '397 days, 6 hours, 44 minutes, 15 seconds, 574 milliseconds'

const getDaysDiffBetweenDates = (dateInitial, dateFinal) =>
  (dateFinal - dateInitial) / (1000 * 3600 * 24);
// 事例
getDaysDiffBetweenDates(new Date('2017-12-13'), new Date('2017-12-22')); // 9

const httpGet = (url, callback, err = console.error) => {
  const request = new XMLHttpRequest();
  request.open('GET', url, true);
  request.onload = () => callback(request.responseText);
  request.onerror = () => err(request);
  request.send();
};
httpGet(
  'https://jsonplaceholder.typicode.com/posts/1',
  console.log
); 
// {"userId": 1, "id": 1, "title": "sample title", "body": "my text"}

const httpPost = (url, data, callback, err = console.error) => {
  const request = new XMLHttpRequest();
  request.open('POST', url, true);
  request.setRequestHeader('Content-type', 'application/json; charset=utf-8');
  request.onload = () => callback(request.responseText);
  request.onerror = () => err(request);
  request.send(data);
};
const newPost = {
  userId: 1,
  id: 1337,
  title: 'Foo',
  body: 'bar bar bar'
};
const data = JSON.stringify(newPost);
httpPost(
  'https://jsonplaceholder.typicode.com/posts',
  data,
  console.log
); 
// {"userId": 1, "id": 1337, "title": "Foo", "body": "bar bar bar"}

const counter = (selector, start, end, step = 1, duration = 2000) => {
  let current = start,
    _step = (end - start) * step < 0 ? -step : step,
    timer = setInterval(() => {
      current += _step;
      document.querySelector(selector).innerHTML = current;
      if (current >= end) document.querySelector(selector).innerHTML = end;
      if (current >= end) clearInterval(timer);
    }, Math.abs(Math.floor(duration / (end - start))));
  return timer;
};
// 事例
counter('#my-id', 1, 1000, 5, 2000); 
// 让 `id=“my-id”`的元素创建一个2秒计时器

const el = document.createElement('textarea');
  el.value = str;
  el.setAttribute('readonly', '');
  el.style.position = 'absolute';
  el.style.left = '-9999px';
  document.body.appendChild(el);
  const selected =
    document.getSelection().rangeCount > 0 ? document.getSelection().getRangeAt(0) : false;
  el.select();
  document.execCommand('copy');
  document.body.removeChild(el);
  if (selected) {
    document.getSelection().removeAllRanges();
    document.getSelection().addRange(selected);
  }
};
// 事例
copyToClipboard('Lorem ipsum'); 
// 'Lorem ipsum' copied to clipboard

const isBrowserTabFocused = () => !document.hidden;
// 事例
isBrowserTabFocused(); // true

const fs = require('fs');
const createDirIfNotExists = dir => (!fs.existsSync(dir) ? fs.mkdirSync(dir) : undefined);
// 事例
createDirIfNotExists('test');