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

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、如何评价滚动到页面顶部？

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

最后混子前端提前祝大家2020圣诞快乐，本章完~