这篇文章基于实际使用场景总结了24个ES6代码段，可用来解决项目中可能遇到的一系列问题。

1. 如何隐藏所有指定元素？

const hide = (...el) => [...el].forEach(e => (e.style.display = 'none'));
// Example
hide(document.querySelectorAll('img')); // 隐藏页面上的所有 <img> 元素

2. 如何确认元素是否具有指定的类？

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

3. 如何切换元素的类？

const toggleClass = (el, className) => el.classList.toggle(className);
// Example
toggleClass(document.querySelector('p.special'), 'special'); 
// 该段不再有 'special' 类

4. 如何获取当前页面的滚动位置？

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

5. 如何平滑滚动到页面顶部？

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

6. 如何确认父元素是否包含子元素？

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

7. 如何确认指定元素是否在视口可见？

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;
};
// Examples
elementIsVisibleInViewport(el); // (不完全可见)
elementIsVisibleInViewport(el, true); // (部分可见)

8. 如何获取一个元素内的所有图像？

const getImages = (el, includeDuplicates = false) => {
  const images = [...el.getElementsByTagName('img')].map(img => img.getAttribute('src'));
  return includeDuplicates ? images : [...new Set(images)];
};
// Examples
getImages(document, true); // ['image1.jpg', 'image2.png', 'image1.png', '...']
getImages(document, false); // ['image1.jpg', 'image2.png', '...']

9. 如何分辨设备是移动设备还是桌面设备？

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

10. 如何获取当前URL？

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

11. 如何创建一个包含当前URL参数的对象？

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

12. 如何将一组表单元素编码为一个对象？

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

13. 如何从对象中检索给定选择器指示的一组属性？

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']

14. 如何在等待一定时间后调用提供的函数（单位毫秒）？

const delay = (fn, wait, ...args) => setTimeout(fn, wait, ...args);
delay(
  function(text) {
    console.log(text);
  },
  1000,
  'later'
); 
// 一秒后记录 'later' 。

15. 如何在给定元素上触发特定事件，且可选传递自定义数据？

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

16. 如何移除一个元素的事件侦听器？

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); // no longer logs '!' upon clicking on the page

17. 如何获得给定毫秒数的可读格式？

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(', ');
};
// Examples
formatDuration(1001); // '1 second, 1 millisecond'
formatDuration(34325055574); // '397 days, 6 hours, 44 minutes, 15 seconds, 574 milliseconds'

18. 如何获取两个日期之间的天数间隔？

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

19. 如何对传递的URL进行GET请求？

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
); 
// Logs: {"userId": 1, "id": 1, "title": "sample title", "body": "my text"}

20. 如何对传递的URL进行POST请求？

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
); 
// Logs: {"userId": 1, "id": 1337, "title": "Foo", "body": "bar bar bar"}

21. 如何为指定选择器创建具有指定范围、步长和持续时间的计时器？

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;
};
// Example
counter('#my-id', 1, 1000, 5, 2000); // 为 id="my-id" 的元素创建一个两秒的计时器

22. 如何将一个字符串复制到剪贴板？

const copyToClipboard = str => {
  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);
  }
};
// Example
copyToClipboard('Lorem ipsum'); // 'Lorem ipsum' copied to clipboard.

23. 如何确定页面的浏览器选项卡是否处于前台活跃状态？

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

24. 如果一个目录不存在，如何创建它？

const fs = require('fs');
const createDirIfNotExists = dir => (!fs.existsSync(dir) ? fs.mkdirSync(dir) : undefined);
// Example
createDirIfNotExists('test'); // creates the directory 'test', if it doesn't exist

原文链接：

https://madza.hashnode.dev/24-modern-es6-code-snippets-to-solve-practical-js-problems