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
``
