者: 木子星兮i
轉發鏈接:https://mp.weixin.qq.com/s/36oBZMd-m-2k5EKPghfG3A
勢
通常,我們在html中展示圖片,會有兩種方式:
img的懶加載實現
img有兩種方式實現懶加載:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>event</title> <style> img { background: #F1F1FA; width: 400px; height: 300px; display: block; margin: 10px auto; border: 0; } </style> </head> <body> <img src="https://ik.imagekit.io/demo/img/image1.jpeg?tr=w-400,h-300" /> <img src="https://ik.imagekit.io/demo/img/image2.jpeg?tr=w-400,h-300" /> <img src="https://ik.imagekit.io/demo/img/image3.jpg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image2.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image3.jpg?tr=w-400,h-300" /> --> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image4.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image5.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image6.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image7.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image8.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image9.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image10.jpeg?tr=w-400,h-300" /> <script> document.addEventListener("DOMContentLoaded", function() { var lazyloadImages=document.querySelectorAll("img.lazy"); var lazyloadThrottleTimeout; function lazyload () { if(lazyloadThrottleTimeout) { clearTimeout(lazyloadThrottleTimeout); } lazyloadThrottleTimeout=setTimeout(function() { var scrollTop=window.pageYOffset; lazyloadImages.forEach(function(img) { if(img.offsetTop < (window.innerHeight + scrollTop)) { img.src=img.dataset.src; img.classList.remove('lazy'); } }); if(lazyloadImages.length==0) { document.removeEventListener("scroll", lazyload); window.removeEventListener("resize", lazyload); window.removeEventListener("orientationChange", lazyload); } }, 20); } document.addEventListener("scroll", lazyload); window.addEventListener("resize", lazyload); window.addEventListener("orientationChange", lazyload); }); </script> </body> </html>
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>observer</title> <style> img { background: #F1F1FA; width: 400px; height: 300px; display: block; margin: 10px auto; border: 0; } </style> </head> <body> <img src="https://ik.imagekit.io/demo/img/image2.jpeg?tr=w-400,h-300" /> <img src="https://ik.imagekit.io/demo/img/image3.jpg?tr=w-400,h-300" /> --> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image1.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image2.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image3.jpg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image4.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image5.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image6.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image7.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image8.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image9.jpeg?tr=w-400,h-300" /> <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image10.jpeg?tr=w-400,h-300" /> <script> document.addEventListener("DOMContentLoaded", function() { var lazyloadImages=document.querySelectorAll(".lazy"); var imageObserver=new IntersectionObserver(function(entries, observer) { entries.forEach(function(entry) { if (entry.isIntersecting) { var image=entry.target; image.src=image.dataset.src; image.classList.remove("lazy"); imageObserver.unobserve(image); } }); }); lazyloadImages.forEach(function(image) { imageObserver.observe(image); }); }); </script> </body> </html>
background-image的實現
background-image的實現跟img的原理基本是一樣的,區別是在對class的處理上:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>background</title> <style> body { margin: 0; } .bg { height: 200px; } #bg-image.lazy { background-image: none; background-color: #F1F1FA; } #bg-image { background-image: url("https://ik.imagekit.io/demo/img/image1.jpeg?tr=w-400,h-300"); background-size: 100%; } </style> </head> <body> <div id="bg-image" class="bg lazy"></div> <div id="bg-image" class="bg lazy"></div> <div id="bg-image" class="bg lazy"></div> <div id="bg-image" class="bg lazy"></div> <div id="bg-image" class="bg lazy"></div> <div id="bg-image" class="bg lazy"></div> <div id="bg-image" class="bg lazy"></div> <div id="bg-image" class="bg lazy"></div> <script> document.addEventListener("DOMContentLoaded", function() { var lazyloadImages=document.querySelectorAll(".lazy"); var imageObserver=new IntersectionObserver(function(entries, observer) { entries.forEach(function(entry) { if (entry.isIntersecting) { var image=entry.target; image.classList.remove("lazy"); imageObserver.unobserve(image); } }); }); lazyloadImages.forEach(function(image) { imageObserver.observe(image); }); }); </script> </body> </html>
漸進式懶加載
漸進式懶加載,指的是存在降級處理,通常html形式如下:
<a href="full.jpg" class="progressive replace"> <img src="tiny.jpg" class="preview" alt="image" /> </a>
這樣的代碼會有2個好處:
最終的代碼如下:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>progressive</title> <style> a.progressive { position: relative; display: block; overflow: hidden; outline: none; } a.progressive:not(.replace) { cursor: default; } a.progressive img { display: block; width: 100%; max-width: none; height: auto; border: 0 none; } a.progressive img.preview { filter: blur(2vw); transform: scale(1.05); } a.progressive img.reveal { position: absolute; left: 0; top: 0; will-change: transform, opacity; animation: reveal 1s ease-out; } @keyframes reveal { 0% {transform: scale(1.05); opacity: 0;} 100% {transform: scale(1); opacity: 1;} } </style> </head> <body> <a href="http://m.jungjaehyung.com/uploadfile/2024/1009/20241009120959593.jpg" data-srcset="http://m.jungjaehyung.com/uploadfile/2024/1009/20241009120959593.jpg 800w, https://s3-us-west-2.amazonaws.com/s.cdpn.io/123941/nature5big.jpg 1600w" class="progressive replace"> <img src="data:image/jpeg;base64,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" class="preview" alt="palm trees" /> </a> <a href="http://m.jungjaehyung.com/uploadfile/2024/1009/20241009121000935.jpg" class="progressive replace"> <img src="http://lorempixel.com/20/15/nature/2/" class="preview" alt="sunset" /> </a> <a href="http://m.jungjaehyung.com/uploadfile/2024/1009/20241009121001477.jpg" class="progressive replace"> <img src="http://lorempixel.com/20/15/nature/3/" class="preview" alt="tide" /> </a> <a href="http://m.jungjaehyung.com/uploadfile/2024/1009/20241009120959593.jpg" data-srcset="http://m.jungjaehyung.com/uploadfile/2024/1009/20241009120959593.jpg 800w, https://s3-us-west-2.amazonaws.com/s.cdpn.io/123941/nature5big.jpg 1600w" class="progressive replace"> <img src="data:image/jpeg;base64,/9j/4AAQSkZJRgABAQEAYABgAAD//gA7Q1JFQVRPUjogZ2QtanBlZyB2MS4wICh1c2luZyBJSkcgSlBFRyB2NjIpLCBxdWFsaXR5ID0gNzAK/9sAQwAKBwcIBwYKCAgICwoKCw4YEA4NDQ4dFRYRGCMfJSQiHyIhJis3LyYpNCkhIjBBMTQ5Oz4+PiUuRElDPEg3PT47/9sAQwEKCwsODQ4cEBAcOygiKDs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7/8AAEQgABQAUAwEiAAIRAQMRAf/EAB8AAAEFAQEBAQEBAAAAAAAAAAABAgMEBQYHCAkKC//EALUQAAIBAwMCBAMFBQQEAAABfQECAwAEEQUSITFBBhNRYQcicRQygZGhCCNCscEVUtHwJDNicoIJChYXGBkaJSYnKCkqNDU2Nzg5OkNERUZHSElKU1RVVldYWVpjZGVmZ2hpanN0dXZ3eHl6g4SFhoeIiYqSk5SVlpeYmZqio6Slpqeoqaqys7S1tre4ubrCw8TFxsfIycrS09TV1tfY2drh4uPk5ebn6Onq8fLz9PX29/j5+v/EAB8BAAMBAQEBAQEBAQEAAAAAAAABAgMEBQYHCAkKC//EALURAAIBAgQEAwQHBQQEAAECdwABAgMRBAUhMQYSQVEHYXETIjKBCBRCkaGxwQkjM1LwFWJy0QoWJDThJfEXGBkaJicoKSo1Njc4OTpDREVGR0hJSlNUVVZXWFlaY2RlZmdoaWpzdHV2d3h5eoKDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uLj5OXm5+jp6vLz9PX29/j5+v/aAAwDAQACEQMRAD8A5yC3e2S3gM7OEQHdgA57VTuLAPqUoaUk7yM7R2BPSiivS5VN8stjmk2ldGVM3lyshG7bxk0UUV4skk2jdN2P/9k=" class="preview" alt="palm trees" /> </a> <a href="http://m.jungjaehyung.com/uploadfile/2024/1009/20241009121000935.jpg" class="progressive replace"> <img src="http://lorempixel.com/20/15/nature/2/" class="preview" alt="sunset" /> </a> <a href="http://m.jungjaehyung.com/uploadfile/2024/1009/20241009121001477.jpg" class="progressive replace"> <img src="http://lorempixel.com/20/15/nature/3/" class="preview" alt="tide" /> </a> <script> window.addEventListener('load', function() { var pItem=document.getElementsByClassName('progressive replace'), timer; window.addEventListener('scroll', scroller, false); window.addEventListener('resize', scroller, false); inView(); function scroller(e) { timer=timer || setTimeout(function() { timer=null; requestAnimationFrame(inView); }, 300); } function inView() { var scrollTop=window.pageYOffset; var innerHeight=window.innerHeight; var p=0; while (p < pItem.length) { var offsetTop=pItem[p].offsetTop; if (offsetTop < (scrollTop + innerHeight)) { loadFullImage(pItem[p]); pItem[p].classList.remove('replace'); } else p++; } } function loadFullImage(item) { var img=new Image(); if (item.dataset) { img.srcset=item.dataset.srcset || ''; img.sizes=item.dataset.sizes || ''; } img.src=item.href; img.className='reveal'; if (img.complete) addImg(); else img.onload=addImg; function addImg() { item.addEventListener('click', function(e) { e.preventDefault(); }, false); item.appendChild(img).addEventListener('animationend', function(e) { var pImg=item.querySelector('img.preview'); if (pImg) { e.target.alt=pImg.alt || ''; item.removeChild(pImg); e.target.classList.remove('reveal'); } }); } } }, false); </script> </body> </html>
現成庫
推薦下面這個庫,使用非常簡單:https://www.npmjs.com/package/lozad
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為 `src` 賦值成一個通用的預覽圖,下拉時候再動態賦值成正式的圖片。
`preview.png`是預覽圖片,比較小,加載很快,而且很多圖片都共用這個`preview.png`,加載一次即可。
待頁面下拉,圖片顯示出來時,再去替換`src`為`data-realsrc`的值。
<img src="preview.png" data-realsrc="abc.png"/>
這里為何要用`data-`開頭的屬性值?
所有 HTML 中自定義的屬性,都應該用`data-`開頭,因為`data-`開頭的屬性瀏覽器渲染的時候會忽略掉,提高渲染性能。
*請認真填寫需求信息,我們會在24小時內與您取得聯系。