记好这24个ES6方法，用于解决实际开发的JS问题

window.requestAnimationFrame() 告诉浏览器-你希望执行一个动画，并且要求浏览器在下一重绘之前调用指定的函数更新动画。之前执行。

requestAnimationFrame：优势：由系统决定决定功能的执行时机。60Hz的刷新频率，然后每次刷新的间隔中会执行一次替换函数，不会引起丢帧，不会卡顿。

1 const elementContains = (parent, child) => parent !== child && parent.contains(child);
2 
3 // 事例
4 elementContains(document.querySelector(‘head‘), document.querySelector(‘title‘)); 
5 // true
6 elementContains(document.querySelector(‘body‘), document.querySelector(‘body‘)); 
7 // false

 1 const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
 2   const { top, left, bottom, right } = el.getBoundingClientRect();
 3   const { innerHeight, innerWidth } = window;
 4   return partiallyVisible
 5     ? ((top > 0 && top  0 && bottom  6         ((left > 0 && left  0 && right  innerWidth))
 7     : top >= 0 && left >= 0 && bottom  innerWidth;
 8 };
 9 
10 // 事例
11 elementIsVisibleInViewport(el); // 需要左右可见
12 elementIsVisibleInViewport(el, true); // 需要全屏(上下左右)可以见

1 const getImages = (el, includeDuplicates = false) => {
2   const images = [...el.getElementsByTagName(‘img‘)].map(img => img.getAttribute(‘src‘));
3   return includeDuplicates ? images : [...new Set(images)];
4 };
5 
6 // 事例：includeDuplicates 为 true 表示需要排除重复元素
7 getImages(document, true); // [‘image1.jpg‘, ‘image2.png‘, ‘image1.png‘, ‘...‘]
8 getImages(document, false); // [‘image1.jpg‘, ‘image2.png‘, ‘...‘]

1 const detectDeviceType = () =>
2   /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)
3     ? ‘Mobile‘
4     : ‘Desktop‘;
5 
6 // 事例
7 detectDeviceType(); // "Mobile" or "Desktop"

1 const currentURL = () => window.location.href
2 
3 // 事例
4 currentURL() // ‘https://google.com‘

1 const getURLParameters = url =>
2   (url.match(/([^?=&]+)(=([^&]*))/g) || []).reduce(
3     (a, v) => ((a[v.slice(0, v.indexOf(‘=‘))] = v.slice(v.indexOf(‘=‘) + 1)), a),
4     {}
5   );
6 
7 // 事例
8 getURLParameters(‘http://url.com/page?n=Adam&s=Smith‘); // {n: ‘Adam‘, s: ‘Smith‘}
9 getURLParameters(‘google.com‘); // {}

 1 const formToObject = form =>
 2   Array.from(new FormData(form)).reduce(
 3     (acc, [key, value]) => ({
 4       ...acc,
 5       [key]: value
 6     }),
 7     {}
 8   );
 9 
10 // 事例
11 formToObject(document.querySelector(‘#form‘)); 
12 // { email: ‘test@email.com‘, name: ‘Test Name‘ }

 1 const get = (from, ...selectors) =>
 2   [...selectors].map(s =>
 3     s
 4       .replace(/\[([^\[\]]*)\]/g, ‘.$1.‘)
 5       .split(‘.‘)
 6       .filter(t => t !== ‘‘)
 7       .reduce((prev, cur) => prev && prev[cur], from)
 8   );
 9 const obj = { selector: { to: { val: ‘val to select‘ } }, target: [1, 2, { a: ‘test‘ }] };
10 
11 // Example
12 get(obj, ‘selector.to.val‘, ‘target[0]‘, ‘target[2].a‘); 
13 // [‘val to select‘, 1, ‘test‘]

 1 const delay = (fn, wait, ...args) => setTimeout(fn, wait, ...args);
 2 delay(
 3   function(text) {
 4     console.log(text);
 5   },
 6   1000,
 7   ‘later‘
 8 ); 
 9 
10 // 1秒后打印 ‘later‘

1 const triggerEvent = (el, eventType, detail) =>
2   el.dispatchEvent(new CustomEvent(eventType, { detail }));
3 
4 // 事例
5 triggerEvent(document.getElementById(‘myId‘), ‘click‘);
6 triggerEvent(document.getElementById(‘myId‘), ‘click‘, { username: ‘bob‘ });

 1 // 向 window派发一个resize内置事件
 2 window.dispatchEvent(new Event(‘resize‘))
 3  
 4 
 5 // 直接自定义事件，使用 Event 构造函数：
 6 var event = new Event(‘build‘);
 7 var elem = document.querySelector(‘#id‘)
 8 // 监听事件
 9 elem.addEventListener(‘build‘, function (e) { ... }, false);
10 // 触发事件.
11 elem.dispatchEvent(event);

1 var myEvent = new CustomEvent(eventname, options);
2 其中 options 可以是：
3 {
4   detail: {
5     ...
6   },
7   bubbles: true,    //是否冒泡
8   cancelable: false //是否取消默认事件
9 }

1 element.dispatchEvent(customEvent);

 1 // add an appropriate event listener
 2 obj.addEventListener("cat", function(e) { process(e.detail) });
 3  
 4 // create and dispatch the event
 5 var event = new CustomEvent("cat", {"detail":{"hazcheeseburger":true}});
 6 obj.dispatchEvent(event);
 7 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：
 8 
 9 // 绑定自定义事件
10 $(element).on(‘myCustomEvent‘, function(){});
11  
12 // 触发事件
13 $(element).trigger(‘myCustomEvent‘);
14 // 此外，你还可以在触发自定义事件时传递更多参数信息：
15  
16 $( "p" ).on( "myCustomEvent", function( event, myName ) {
17   $( this ).text( myName + ", hi there!" );
18 });
19 $( "button" ).click(function () {
20   $( "p" ).trigger( "myCustomEvent", [ "John" ] );
21 });

1 const off = (el, evt, fn, opts = false) => el.removeEventListener(evt, fn, opts);
2 
3 const fn = () => console.log(‘!‘);
4 document.body.addEventListener(‘click‘, fn);
5 off(document.body, ‘click‘, fn); 

 1 const formatDuration = ms => {
 2   if (ms ms;
 3   const time = {
 4     day: Math.floor(ms / 86400000),
 5     hour: Math.floor(ms / 3600000) % 24,
 6     minute: Math.floor(ms / 60000) % 60,
 7     second: Math.floor(ms / 1000) % 60,
 8     millisecond: Math.floor(ms) % 1000
 9   };
10   return Object.entries(time)
11     .filter(val => val[1] !== 0)
12     .map(([key, val]) => `${val} ${key}${val !== 1 ? ‘s‘ : ‘‘}`)
13     .join(‘, ‘);
14 };
15 
16 // 事例
17 formatDuration(1001); // ‘1 second, 1 millisecond‘
18 formatDuration(34325055574); 
19 // ‘397 days, 6 hours, 44 minutes, 15 seconds, 574 milliseconds‘

1 const getDaysDiffBetweenDates = (dateInitial, dateFinal) =>
2   (dateFinal - dateInitial) / (1000 * 3600 * 24);
3 
4 // 事例
5 getDaysDiffBetweenDates(new Date(‘2017-12-13‘), new Date(‘2017-12-22‘)); // 9

 1 const httpGet = (url, callback, err = console.error) => {
 2   const request = new XMLHttpRequest();
 3   request.open(‘GET‘, url, true);
 4   request.onload = () => callback(request.responseText);
 5   request.onerror = () => err(request);
 6   request.send();
 7 };
 8 
 9 httpGet(
10   ‘https://jsonplaceholder.typicode.com/posts/1‘,
11   console.log
12 ); 
13 
14 // {"userId": 1, "id": 1, "title": "sample title", "body": "my text"}

 1 const httpPost = (url, data, callback, err = console.error) => {
 2   const request = new XMLHttpRequest();
 3   request.open(‘POST‘, url, true);
 4   request.setRequestHeader(‘Content-type‘, ‘application/json; charset=utf-8‘);
 5   request.onload = () => callback(request.responseText);
 6   request.onerror = () => err(request);
 7   request.send(data);
 8 };
 9 
10 const newPost = {
11   userId: 1,
12   id: 1337,
13   title: ‘Foo‘,
14   body: ‘bar bar bar‘
15 };
16 const data = JSON.stringify(newPost);
17 httpPost(
18   ‘https://jsonplaceholder.typicode.com/posts‘,
19   data,
20   console.log
21 ); 
22 
23 // {"userId": 1, "id": 1337, "title": "Foo", "body": "bar bar bar"}

 1 const counter = (selector, start, end, step = 1, duration = 2000) => {
 2   let current = start,
 3     _step = (end - start) * step step : step,
 4     timer = setInterval(() => {
 5       current += _step;
 6       document.querySelector(selector).innerHTML = current;
 7       if (current >= end) document.querySelector(selector).innerHTML = end;
 8       if (current >= end) clearInterval(timer);
 9     }, Math.abs(Math.floor(duration / (end - start))));
10   return timer;
11 };
12 
13 // 事例
14 counter(‘#my-id‘, 1, 1000, 5, 2000); 
15 // 让 `id=“my-id”`的元素创建一个2秒计时器

 1   const el = document.createElement(‘textarea‘);
 2   el.value = str;
 3   el.setAttribute(‘readonly‘, ‘‘);
 4   el.style.position = ‘absolute‘;
 5   el.style.left = ‘-9999px‘;
 6   document.body.appendChild(el);
 7   const selected =
 8     document.getSelection().rangeCount > 0 ? document.getSelection().getRangeAt(0) : false;
 9   el.select();
10   document.execCommand(‘copy‘);
11   document.body.removeChild(el);
12   if (selected) {
13     document.getSelection().removeAllRanges();
14     document.getSelection().addRange(selected);
15   }
16 };
17 
18 // 事例
19 copyToClipboard(‘Lorem ipsum‘); 
20 // ‘Lorem ipsum‘ copied to clipboard

1 const isBrowserTabFocused = () => !document.hidden;
2 
3 // 事例
4 isBrowserTabFocused(); // true

1 const fs = require(‘fs‘);
2 const createDirIfNotExists = dir => (!fs.existsSync(dir) ? fs.mkdirSync(dir) : undefined);
3 
4 // 事例
5 createDirIfNotExists(‘test‘);