混子前端24个ES6代码片段

**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？

```js
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？

```js
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？

```js
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？

```js
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？

```js
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？

```js
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？

```js
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？

```js
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？

## 10、如何获取当前 URL？

```js
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？

```js
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？

```js
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？

```js
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）？

```js
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？

```js
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？

```js
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？

```js
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？

```js
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？

```js
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？

```js
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？

```js
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？

```js
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？

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

// Example 
isBrowserTabFocused(); // true
```

## 24、如果一个目录不存在，如何创建它？

```js
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
```