最近在整理电脑的项目，总结了一些常见的小功能（获取URL、URL参数解析、Form表单数据解析等），特别的reduce方法的妙用。

1.如何批量隐藏指定的元素？

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

// 调用示例
hide(document.querySelectorAll("img"));

2.如何检查元素是否具有指定的类？

const hasClass = (el, className) => el.classList.contains(className);

// 调用示例
hasClass(document.querySelector("p.special"), "special"); // true

3.如何切换元素的样式类？

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

// 调用示例
toggleClass(document.querySelector("p.special"), "special");

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,
});

// 调用示例
getScrollPosition(); // {x: 0, y: 100}

5.如何平滑滚动到页面顶部？

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

// 调用示例
scrollToTop();

6.如何检查父元素是否包含子元素？

const elementContains = (parent, child) =>
    parent !== child && parent.contains(child);

// 调用示例
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窗中是否可见？

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;
};

// 调用示例
elementIsVisibleInViewport(el); // 不完全可见
elementIsVisibleInViewport(el, true); // 部分可见

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)];
};

// 调用示例
getImages(document, true); // ['image1.jpg', 'image2.png', 'image1.png', '...']
getImages(document, false); // ['image1.jpg', 'image2.png', '...']

9.如何确定该设备是移动设备还是桌面端？

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

// 调用示例
detectDeviceType(); // "移动端" or "桌面"

10.如何获取当前URL？

const currentURL = () => window.location.href;

// 调用示例
currentURL();

11.将URL参数解析为对象？

const getURLParameters = (url) =>
    (url.match(/([^?=&]+)(=([^&]*))/g) || []).reduce(
        (a, v) => (
            (a[v.slice(0, v.indexOf("="))] = v.slice(v.indexOf("=") + 1)), a
        ),
        {}
    );

// 调用示例
getURLParameters("http://url.com/page?n=DevPoint&s=Shenzhen"); // {n: 'DevPoint', s: 'Shenzhen'}
getURLParameters("baidu.com"); // {}

12.如何将Form表单数据转为对象?

const formToObject = (form) =>
    Array.from(new FormData(form)).reduce(
        (account, [key, value]) => ({
            ...account,
            [key]: value,
        }),
        {}
    );

// 调用示例
formToObject(document.querySelector("#form")); // { city: 'Shenzhen', name: 'DevPoint' }

13.延迟执行函数（毫秒）?

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

14.如何删除DOM事件？

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);

15.如何将时间戳转为直观的时间格式？

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,
    };
    const timeZh = {
        day: "天",
        hour: "小时",
        minute: "分钟",
        second: "秒",
        millisecond: "毫秒",
    };
    return Object.entries(time)
        .filter((val) => val[1] !== 0)
        .map(([key, val]) => `${val} ${timeZh[key]}`)
        .join("，");
};

// 调用示例
formatDuration(1001); // 1 秒，1 毫秒
formatDuration(34325055574); // 397 天，6 小时，44 分钟，15 秒，574 毫秒

16.如何获得两个日期的时间差？

const getDaysDiffBetweenDates = (dateInitial, dateFinal) =>
    (dateFinal - dateInitial) / (1000 * 3600 * 24);

// 调用示例，以天计算
getDaysDiffBetweenDates(new Date("2021-03-20"), new Date("2021-04-03")); // 14

17.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);
    }
};

// 调用示例
copyToClipboard("DevPoint"); // 'DevPoint' copied to clipboard.

18.如何创建一个计数器？

指定一个DOM id，创建一个计数器，指定步长，结束数值，按照同样的频率计数。

const counter = (selector, start, end, step = 1, duration = 2000) => {
    let current = start;
    const _step = (end - start) * step < 0 ? -step : step;
    const 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;
};

// 调用示例
counter("#counter", 1, 1000, 5, 2000); // 创建一个计数器，从1开始，步长为5，计数到1000结束

完