Advanced Lazy Loading Strategies

Definitions

• Lazy Loading: A technique that delays the loading of images or other media until they are needed (e.g., when they come into the viewport).
• Intersection Observer: A browser API that allows you to configure a callback function to be executed when a target element intersects with the viewport.
• Placeholder Image: A low-resolution image or a simple loading spinner shown while the actual image is being loaded.

1. Native Lazy Loading

HTML5 introduced native lazy loading for images. Simply add the loading="lazy" attribute to your <img> tags.

<img src="image.jpg" loading="lazy" alt="Description">

2. Intersection Observer API

Use the Intersection Observer to load images when they enter the viewport.

const images = document.querySelectorAll('img[data-src]');
const config = {
    rootMargin: '0px 0px 50px 0px',
    threshold: 0
};

let observer = new IntersectionObserver((entries, observer) => {
    entries.forEach(entry => {
        if (entry.isIntersecting) {
            const img = entry.target;
            img.src = img.dataset.src;
            img.onload = () => img.classList.add('fade-in');
            observer.unobserve(img);
        }
    });
}, config);

images.forEach(image => {
    observer.observe(image);
});
            

3. Placeholder Images

While the high-resolution image loads, display a low-resolution version or a loading spinner.

4. Progressive Loading

Load images progressively as the user scrolls through the page to enhance perceived performance.

Key Points

• Ensure that your lazy-loaded images have width and height attributes to prevent layout shifts.
• Test on various devices and browsers to ensure compatibility.
• Use a fallback for browsers that do not support lazy loading.
• Optimize images for web to reduce load times.