Lazy Loading Images - A Comprehensive Guide

Lazy loading is a technique used in web development to defer the loading of non-essential resources at the initial page load. This means images (or other resources) are only loaded when they are about to enter the viewport. This can significantly improve the initial load time of your webpage, making it faster and more efficient.

How Lazy Loading Works

Lazy loading works by deferring the loading of images until they are needed. This is typically done using JavaScript to detect when an image is about to enter the viewport, and then dynamically loading the image source. This reduces the number of HTTP requests during the initial page load and decreases page load time.

Pros and Cons of Lazy Loading

Pros

• Improves initial page load time
• Reduces bandwidth usage
• Enhances user experience, especially on slow networks

Cons

• Requires JavaScript to be enabled
• Can complicate SEO if not implemented correctly
• May cause delays in image loading when scrolling quickly

Steps to Implement Lazy Loading

Here are the steps to implement lazy loading for images using JavaScript and the Intersection Observer API.

Step 1: Add the HTML

        
            <img src="placeholder.jpg" data-src="actual-image.jpg" class="lazyload">
        
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Step 2: Add the JavaScript

        
            document.addEventListener("DOMContentLoaded", function() {
                let lazyImages = [].slice.call(document.querySelectorAll("img.lazyload"));
            
                if ("IntersectionObserver" in window) {
                    let lazyImageObserver = new IntersectionObserver(function(entries, observer) {
                        entries.forEach(function(entry) {
                            if (entry.isIntersecting) {
                                let lazyImage = entry.target;
                                lazyImage.src = lazyImage.dataset.src;
                                lazyImage.classList.remove("lazyload");
                                lazyImageObserver.unobserve(lazyImage);
                            }
                        });
                    });
            
                    lazyImages.forEach(function(lazyImage) {
                        lazyImageObserver.observe(lazyImage);
                    });
                }
            });
        
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