解决实际问题的ES6代码段

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  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('hide'));  
      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