How to implement lazy loading of images in js

This article will give you a detailed introduction to the js method of lazy loading of images. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to everyone.

Lazy loading of images is something that front-end optimization must master. Lazy loading of images can save bandwidth and reduce the load on our web pages. Next, I will record the method I have mastered for lazy loading of images. First of all, one way it is implemented is that the src of our picture within the view window is loaded first, but the src that is not within the view window will not be loaded as our scroll bar slides down.

Come down and load

The way I implement it is to use weapi, which is relatively simple. InstersectionObserver (official website InstersectionObserver).
Let’s go directly to the code

<div>
			<img  data-src="https://ss0.bdstatic.com/70cFvHSh_Q1YnxGkpoWK1HF6hhy/it/u=3225163326,3627210682&fm=26&gp=0.jpg" alt="How to implement lazy loading of images in js" >
			<img  data-src="https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=3228549874,2173006364&fm=26&gp=0.jpg" alt="How to implement lazy loading of images in js" >
			<img  data-src="https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=1246451335,909670857&fm=26&gp=0.jpg" alt="How to implement lazy loading of images in js" >
			<img  data-src="https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=3609981743,3469269943&fm=26&gp=0.jpg" alt="How to implement lazy loading of images in js" >
			<img  data-src="https://ss0.bdstatic.com/70cFvHSh_Q1YnxGkpoWK1HF6hhy/it/u=3225163326,3627210682&fm=26&gp=0.jpg" alt="How to implement lazy loading of images in js" >
			<img  data-src="https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=3228549874,2173006364&fm=26&gp=0.jpg" alt="How to implement lazy loading of images in js" >
			<img  data-src="https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=1246451335,909670857&fm=26&gp=0.jpg" alt="How to implement lazy loading of images in js" >
			<img  data-src="https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=3609981743,3469269943&fm=26&gp=0.jpg" alt="How to implement lazy loading of images in js" >
		</div>

js part

//获取全部图片的数组
const imgs = [...document.getElementsByTagName('img')]
		// IntersectionObserver
		if(IntersectionObserver){
			let lazyloadObser = new IntersectionObserver((entries,observer)=>{
				entries.forEach((entry,index) =>{
					let lazyImage = entry.target
					if(entry.intersectionRatio>0){
						lazyImage.src = lazyImage.getAttribute('data-src');
						lazyloadObser.unobserve(lazyImage)
					}
				})
			})	
		  for(let i = 0; i < imgs.length;i++){
			  lazyloadObser.observe(imgs[i])
		  }	
		}

[Recommended learning: javascript advanced tutorial]

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