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24个解决实际问题的ES6代码片段(小结)

三木的旅行日记 人气:0

这是从30 seconds of code中挑出来的非常有用的一些代码片段,这是一个非常棒的项目,大家可以去github上去搜索一下,给个star。

在本文中,我试图根据它们的实际用途对它们进行分类,回答您在项目中可能遇到的常见问题:

1.如何隐藏指定的所有元素?

const hide = (...el) => [...el].forEach(e => (e.style.display = 'none'));

// Example
hide(document.querySelectorAll('img')); // Hides all <img> elements on the page

2.如何检查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.如何为元素切换类?

const toggleClass = (el, className) => el.classList.toggle(className);

// Example
toggleClass(document.querySelector('p.special'), 'special'); 
// The paragraph will not have the 'special' class anymore

这里使用了classList.toggle()方法

toggle( String [, force] )

当只有一个参数时:切换类值;也就是说,即如果类值存在,则删除它并返回 false,如果不存在,则添加它并返回 true。
当存在第二个参数时:若第二个参数的执行结果为 true,则添加指定的类值,若执行结果为 false,则删除它。

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();

递归的方法不断调用使用scrollToTop(),requestAnimationFrame方法告诉浏览器——你希望执行一个动画,并且要求浏览器在下次重绘之前调用指定的回调函数更新动画。它的回调函数执行次数通常与浏览器屏幕刷新次数相匹配,所以效果会比较平滑。

获取当前页面滚动条纵坐标的位置:document.body.scrollTop与document.documentElement.scrollTop

获取当前页面滚动条横坐标的位置:document.body.scrollLeft与document.documentElement.scrollLeft

6.如何检查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.如何检查指定的元素在视口中是否可见?

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); // (not fully visible)
elementIsVisibleInViewport(el, true); // (partially visible)

传入partiallyVisible参数,区分判断是是部分可见还是全部可见。

Element.getBoundingClientRect()方法返回元素的大小及其相对于视口的位置。

8.如何获取元素中的所有图像?

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.如何确定设备是移动设备还是台式机/笔记本电脑?

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' }

Array.from方法用于将两类对象转为真正的数组。类似数组的对象(array-like object)和可遍历(iterable)的对象(包括 ES6 新增的数据结构 Set 和 Map)。
reducer 函数接收4个参数:

  • Accumulator (acc) (累计器)
  • Current Value (cur) (当前值)
  • Current Index (idx) (当前索引)
  • Source Array (src) (源数组)

13.如何从对象中检索出给定的一组属性?

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.延迟调用提供的函数(以毫秒为单位)

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

// Logs 'later' after one second.

15.如何在给定元素上触发特定事件,并可选地传递自定义数据?

const triggerEvent = (el, eventType, detail) =>
 el.dispatchEvent(new CustomEvent(eventType, { detail }));

// Examples
triggerEvent(document.getElementById('myId'), 'click');
triggerEvent(document.getElementById('myId'), 'click', { username: 'bob' });

构造方法 CustomerEvent() 创建一个新的 CustomEvent 对象。
CustomEvent 事件是由程序创建的,可以有任意自定义功能的事件。

16.如何从元素中移除事件侦听器?

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.将给定的毫秒数转换为可读格式

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.如何得到两个日期之间的差异(以天为单位)

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发出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发出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. 如何为指定的选择器创建具有指定范围、步骤和持续时间的计数器?

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); // Creates a 2-second timer for the element with id="my-id"

22.如何将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.

document.getSelection()返回一个  Selection 对象,表示用户选择的文本范围或光标的当前位置。

23.判断页面的浏览器选项卡是否聚焦

const isBrowserTabFocused = () => !document.hidden;

// Example
isBrowserTabFocused(); // true

24.如果不存在目录,则如何创建

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

// Example
createDirIfNotExists('test'); // creates the directory

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