Ce que cet article vous apporte, c'est quelles sont les méthodes pour implémenter le chargement paresseux ? (Introduction à trois méthodes), il a une certaine valeur de référence. Les amis dans le besoin peuvent s'y référer. J'espère qu'il vous sera utile.
Avantages
Avantages en termes de performances : le navigateur consomme des ressources pour charger les images, le décodage et le rendu. Le chargement paresseux peut économiser la consommation de performances et réduire le temps d'événement de chargement. .
Économisez la bande passante : cela ne nécessite aucune explication.
Habituellement, nous affichons les images en html de deux manières :
balise img
-
css background-image
Implémentation du chargement paresseux d'img
Img propose deux façons d'implémenter le chargement paresseux :
Surveillance des événements ( défilement, redimensionnement, changement d'orientation)
<!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" src="https://ik.imagekit.io/demo/img/image2.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image3.jpg?tr=w-400,h-300" /> -->
<img class="lazy" src="https://ik.imagekit.io/demo/img/image4.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image5.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image6.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image7.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image8.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image9.jpeg?tr=w-400,h-300" />
<img class="lazy" 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>Copier après la connexion
Intersection Observer (problème de compatibilité)
<!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" src="https://ik.imagekit.io/demo/img/image1.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image2.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image3.jpg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image4.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image5.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image6.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image7.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image8.jpeg?tr=w-400,h-300" />
<img class="lazy" src="https://ik.imagekit.io/demo/img/image9.jpeg?tr=w-400,h-300" />
<img class="lazy" 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>Copier après la connexion
Mise en place de background-image
L'implémentation de background-image est fondamentalement la même que img La différence réside dans le traitement des classes :
<!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>
<p id="bg-image" class="bg lazy"></p>
<p id="bg-image" class="bg lazy"></p>
<p id="bg-image" class="bg lazy"></p>
<p id="bg-image" class="bg lazy"></p>
<p id="bg-image" class="bg lazy"></p>
<p id="bg-image" class="bg lazy"></p>
<p id="bg-image" class="bg lazy"></p>
<p id="bg-image" class="bg lazy"></p>
<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>Copier après la connexion
Chargement paresseux progressif
Chargement progressif progressif. Le chargement paresseux fait référence à l'existence d'un traitement de rétrogradation. Habituellement, le format HTML est le suivant :
<a href="full.jpg" class="progressive replace">
<img src="tiny.jpg" class="preview" alt="image" />
</a>
Copier après la connexion
Un tel code aura 2 avantages :
-
Si l'exécution de js échoue. , vous pouvez cliquer sur Aperçu
pour utiliser un URI de données d'espace réservé dont la taille est cohérente avec l'image réelle afin d'éviter la redistribution
final Le code est la suivante :
<!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="https://s3-us-west-2.amazonaws.com/s.cdpn.io/123941/nature5.jpg" srcset="https://s3-us-west-2.amazonaws.com/s.cdpn.io/123941/nature5.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="https://s3-us-west-2.amazonaws.com/s.cdpn.io/123941/nature2.jpg" class="progressive replace">
<img src="http://lorempixel.com/20/15/nature/2/" class="preview" alt="sunset" />
</a>
<a href="https://s3-us-west-2.amazonaws.com/s.cdpn.io/123941/nature3.jpg" class="progressive replace">
<img src="http://lorempixel.com/20/15/nature/3/" class="preview" alt="tide" />
</a>
<a href="https://s3-us-west-2.amazonaws.com/s.cdpn.io/123941/nature5.jpg" srcset="https://s3-us-west-2.amazonaws.com/s.cdpn.io/123941/nature5.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="https://s3-us-west-2.amazonaws.com/s.cdpn.io/123941/nature2.jpg" class="progressive replace">
<img src="http://lorempixel.com/20/15/nature/2/" class="preview" alt="sunset" />
</a>
<a href="https://s3-us-west-2.amazonaws.com/s.cdpn.io/123941/nature3.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>Copier après la connexion
Bibliothèque prête à l'emploi
Recommandez la bibliothèque suivante, très simple à utiliser : https://www.npmjs.com/package/lozad
Ce qui précède est le contenu détaillé de. pour plus d'informations, suivez d'autres articles connexes sur le site Web de PHP en chinois!
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