1.如何隱藏所有指定的元素
const hide = (el) => Array.from(el).forEach(e => (e.style.display = 'none'));
// 事例: 隱藏頁(yè)面上所有`<p>`元素
hide(document.querySelectorALL('p'))
2.如何檢查元素是否具有指定的類湿右?
頁(yè)面DOM里面的每個(gè)節(jié)點(diǎn)上都有一個(gè) $\color{#FF0000}{classList}$
對(duì)象,程序員可以使用里面的方法新增票髓、刪除、修改铣耘、查詢節(jié)點(diǎn)上的class類洽沟。
const hasClass = (el, className) => el.classList.contains(className)
// 事例
hasClass(document.querySelector('p.special'), 'spec') // true
3.如何切換一個(gè)元素的類?
const toggleClass = (el, className) => el.classList.toggle(className)
// 事例 移除 p 具有類`special`的 speci 類
toggleClass(document.querySelector('p.special'), 'speci')
4.如何獲取當(dāng)前頁(yè)面的滾動(dòng)位置?
const getScrollPosition = (el = window) => ({
x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft,
y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop
});
// 事例
getScrollPosition(); // {x: 0, y: 200}
5.如何平滑滾動(dòng)到頁(yè)面頂部
const scrollToTop = () => {
const c = document.documentElement.scrollTop || document.body.scrollTop;
if (c > 0) {
window.requestAnimationFrame(scrollToTop);
window.scrollTo(0, c - c / 8);
}
}
// 事例
scrollToTop()
$\color{#FF0000}{window.requestAnimationFrame()}$
告訴瀏覽器——你希望執(zhí)行一個(gè)動(dòng)畫蜗细,并且要求瀏覽器在下次重繪之前調(diào)用指定的回調(diào)函數(shù)更新動(dòng)畫裆操。該方法需要傳入一個(gè)回調(diào)函數(shù)作為參數(shù),該回調(diào)函數(shù)會(huì)在瀏覽器下一次重繪之前執(zhí)行炉媒。
$\color{#FF0000}{requestAnimationFrame:}$
優(yōu)勢(shì):由系統(tǒng)決定回調(diào)函數(shù)的執(zhí)行時(shí)機(jī)踪区。60Hz的刷新頻率,那么每次刷新的間隔中會(huì)執(zhí)行一次回調(diào)函數(shù)橱野,不會(huì)引起丟幀朽缴,不會(huì)卡頓。
6.如何檢查父元素是否包含子元素水援?
const elementContains = (parent, child) => parent !== child && parent.contains(child);
// 事例
elementContains(document.querySelector('head'), document.querySelector('title'));
// true
elementContains(document.querySelector('body'), document.querySelector('body'));
// false
7.如何檢查指定的元素在視口中是否可見?
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;
};
// 事例
elementIsVisibleInViewport(el); // 需要左右可見
elementIsVisibleInViewport(el, true); // 需要全屏(上下左右)可以見
8.如何獲取元素中的所有圖像茅郎?
const getImages = (el, includeDuplicates = false) => {
const images = [...el.getElementsByTagName('img')].map(img => img.getAttribute('src'));
return includeDuplicates ? images : [...new Set(images)];
};
// 事例:includeDuplicates 為 true 表示需要排除重復(fù)元素
getImages(document, true); // ['image1.jpg', 'image2.png', 'image1.png', '...']
getImages(document, false); // ['image1.jpg', 'image2.png', '...']
9.如何確定設(shè)備是移動(dòng)設(shè)備還是臺(tái)式機(jī)/筆記本電腦蜗元?
const detectDeviceType = () =>
/Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)
? 'Mobile'
: 'Desktop';
// 事例
detectDeviceType(); // "Mobile" 移動(dòng)設(shè)備 or "Desktop" 臺(tái)式機(jī)
10.如何創(chuàng)建一個(gè)包含當(dāng)前URL參數(shù)的對(duì)象盆佣?
const getURLParameters = url =>
(url.match(/([^?=&]+)(=([^&]*))/g) || []).reduce(
(a, v) => ((a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1)), a),
{}
);
// 事例
getURLParameters('http://url.com/page?n=Adam&s=Smith'); // {n: 'Adam', s: 'Smith'}
getURLParameters('google.com'); // {}
11.如何將一組表單元素轉(zhuǎn)化為對(duì)象刘急?
const formToObject = form =>
Array.from(new FormData(form)).reduce(
(acc, [key, value]) => ({
...acc,
[key]: value
}),
{}
);
// 事例
formToObject(document.querySelector('#form'));
// { email: 'test@email.com', name: 'Test Name' }
12.如何從對(duì)象檢索給定選擇器指示的一組屬性?
const get = (from, ...selectors) =>
[...selectors].map(s =>
s
.replace(/\[([^\[\]]*)\]/g, '.$1.')
.split('.')
.filter(t => t !== '')
.reduce((prev, cur) => prev && prev[cur], from)
);
const obj = { selector: { to: { val: 'val to select' } }, target: [1, 2, { a: 'test' }] };
// Example
get(obj, 'selector.to.val', 'target[0]', 'target[2].a');
// ['val to select', 1, 'test']
13.如何在等待指定時(shí)間后調(diào)用提供的函數(shù)扁达?
const delay = (fn, wait, ...args) => setTimeout(fn, wait, ...args);
delay(
function(text) {
console.log(text);
},
1000,
'later'
);
// 1秒后打印 'later'
14.如何在給定元素上觸發(fā)特定事件且能選擇地傳遞自定義數(shù)據(jù)掌敬?
const triggerEvent = (el, eventType, detail) =>
el.dispatchEvent(new CustomEvent(eventType, { detail }));
// 事例
triggerEvent(document.getElementById('myId'), 'click');
triggerEvent(document.getElementById('myId'), 'click', { username: 'bob' });
自定義事件的函數(shù)有$\color{#FF0000}{Event}$
惯豆、$\color{#FF0000}{CustomEvent}$
和 $\color{#FF0000}{dispatchEvent}$
// 向 window派發(fā)一個(gè)resize內(nèi)置事件
window.dispatchEvent(new Event('resize'))
// 直接自定義事件,使用 Event 構(gòu)造函數(shù):
var event = new Event('build');
var elem = document.querySelector('#id')
// 監(jiān)聽事件
elem.addEventListener('build', function (e) { ... }, false);
// 觸發(fā)事件.
elem.dispatchEvent(event);
$\color{#FF0000}{CustomEvent}$
可以創(chuàng)建一個(gè)更高度自定義事件奔害,還可以附帶一些數(shù)據(jù)楷兽,具體用法如下:
var myEvent = new CustomEvent(eventname, options);
其中 options 可以是:
{
detail: {
...
},
bubbles: true, //是否冒泡
cancelable: false //是否取消默認(rèn)事件
}
其中 $\color{#FF0000}{detail}$
可以存放一些初始化的信息,可以在觸發(fā)的時(shí)候調(diào)用华临。其他屬性就是定義該事件是否具有冒泡等等功能芯杀。
內(nèi)置的事件會(huì)由瀏覽器根據(jù)某些操作進(jìn)行觸發(fā),自定義的事件就需要人工觸發(fā)雅潭。 $\color{#FF0000}{dispatchEvent}$
函數(shù)就是用來(lái)觸發(fā)某個(gè)事件:
element.dispatchEvent(customEvent);
上面代碼表示揭厚,在 $\color{#FF0000}{element}$
上面觸發(fā) $\color{#FF0000}{customEvent}$
這個(gè)事件。
// add an appropriate event listener
obj.addEventListener("cat", function(e) { process(e.detail) });
// create and dispatch the event
var event = new CustomEvent("cat", {"detail":{"hazcheeseburger":true}});
obj.dispatchEvent(event);
使用自定義事件需要注意兼容性問(wèn)題扶供,而使用 jQuery 就簡(jiǎn)單多了:
// 綁定自定義事件
$(element).on('myCustomEvent', function(){});
// 觸發(fā)事件
$(element).trigger('myCustomEvent');
// 此外筛圆,你還可以在觸發(fā)自定義事件時(shí)傳遞更多參數(shù)信息:
$( "p" ).on( "myCustomEvent", function( event, myName ) {
$( this ).text( myName + ", hi there!" );
});
$( "button" ).click(function () {
$( "p" ).trigger( "myCustomEvent", [ "John" ] );
});
15.如何從元素中移除事件監(jiān)聽器?
const off = (el, evt, fn, opts = false) => el.removeEventListener(evt, fn, opts);
const fn = () => console.log('!');
document.body.addEventListener('click', fn);
off(document.body, 'click', fn);
16.如何獲得給定毫秒數(shù)的可讀格式?
const formatDuration = ms => {
if (ms < 0) ms = -ms;
const time = {
day: Math.floor(ms / 86400000),
hour: Math.floor(ms / 3600000) % 24,
minute: Math.floor(ms / 60000) % 60,
second: Math.floor(ms / 1000) % 60,
millisecond: Math.floor(ms) % 1000
};
return Object.entries(time)
.filter(val => val[1] !== 0)
.map(([key, val]) => `${val} ${key}${val !== 1 ? 's' : ''}`)
.join(', ');
};
// 事例
formatDuration(1001); // '1 second, 1 millisecond'
formatDuration(34325055574);
// '397 days, 6 hours, 44 minutes, 15 seconds, 574 milliseconds'
17.如何獲得兩個(gè)日期之間的差異(以天為單位)椿浓?
const getDaysDiffBetweenDates = (dateInitial, dateFinal) =>
(dateFinal - dateInitial) / (1000 * 3600 * 24);
// 事例
getDaysDiffBetweenDates(new Date('2017-12-13'), new Date('2017-12-22')); // 9
18.如何向傳遞的URL發(fā)出GET請(qǐng)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
);
// {"userId": 1, "id": 1, "title": "sample title", "body": "my text"}
19.如何對(duì)傳遞的URL發(fā)出POST請(qǐng)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
);
// {"userId": 1, "id": 1337, "title": "Foo", "body": "bar bar bar"}
20.如何為指定選擇器創(chuàng)建具有指定范圍太援,步長(zhǎng)和持續(xù)時(shí)間的計(jì)數(shù)器漾岳?
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;
};
// 事例
counter('#my-id', 1, 1000, 5, 2000);
// 讓 `id=“my-id”`的元素創(chuàng)建一個(gè)2秒計(jì)時(shí)器
21.如何將字符串復(fù)制到剪貼板?
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);
}
};
// 事例
copyToClipboard('Lorem ipsum');
// 'Lorem ipsum' copied to clipboard