Have you ever been reading something, and suddenly the content jumps because an image finished loading? This common issue, called Cumulative Layout Shift (CLS), impacts user experience and SEO. Luckily, Next.js offers a smart solution with its Image component.

What is Cumulative Layout Shift (CLS)? 🤔

CLS is a Core Web Vital metric that measures how much unexpected layout shift happens as a page loads. A good CLS score is essential because it means:

✅ Better User Experience
✅ Higher SEO Rankings
✅ A More Professional-Looking Website

The Issue with Standard <img> Tags

Using traditional HTML <img> tags can lead to layout shifts because the browser doesn’t know the image dimensions until it loads. Here’s what typically happens:

1. Page text loads.
2. Image starts downloading.
3. Once loaded, the image pushes content down, causing an annoying “jump.”

Let's see the problem in action:

👆 Watch how content jumps with traditional images (left) vs. stable loading with Next.js Image component (right).

Next.js Image Component to the Rescue 🦸‍♂️

With Next.js’s Image component, you can prevent layout shifts by specifying dimensions up front, giving the browser space to load the image without affecting the layout.

// ✅ Good Practice
import Image from 'next/image';

function ProductCard() {
  return (
    <Image
      src="/product.jpg"
      alt="Product description"
      width={640}
      height={480}
      priority={false}
      loading="lazy"
    />
  );
}

🗝️ Key Features That Prevent Layout Shift

Reserved Space for Smooth Loading

1. Required Dimensions
   
   With the Image component, width and height properties are mandatory. This reserves space for the image even before it loads, preventing layout shifts.

2. Responsive Sizing
   
   The component automatically adapts to the screen size while maintaining the image’s aspect ratio. This prevents layout shifts across different device sizes.

Automatic Placeholder

The Image component can use a blur placeholder, reserving the exact space needed. This allows the layout to stay stable while the image loads, making the experience smoother.

Best Practices for Using the Image Component

Following these practices will help you get the most out of the Next.js Image component.

1. Always Set Dimensions Defining dimensions helps the browser know the exact space the image will take up, avoiding layout shifts.

   // Good
   <Image src="/hero.jpg" width={1200} height={600} alt="Hero image" />

   // Bad (missing dimensions)
   <Image src="/hero.jpg" alt="Hero image" />

1. Use Blur Placeholder for Important Images Adding a blur placeholder for above-the-fold images gives a smooth loading effect.

   <Image src="/hero.jpg" width={1200} height={600} alt="Hero image" placeholder="blur" />

1. Set Priority for Critical Images For hero images or other important visuals, set the priority property to true for faster loading.

   <Image src="/hero.jpg" width={1200} height={600} alt="Hero image" priority />

Check Your CLS Improvements 📊

Use these tools to measure your CLS improvements:

• Chrome DevTools (Performance tab)
• Lighthouse Audits
• Core Web Vitals in Google Search Console

Avoid Common Mistakes ⚠️

1. Don’t Skip Alt Text Alt text is essential for accessibility, making your images accessible to screen readers.

   // Bad
   <Image src="/product.jpg" width={400} height={300} />

   // Good
   <Image src="/product.jpg" width={400} height={300} alt="Red ceramic coffee mug with floral pattern" />

1. Handle External Image URLs Carefully If you’re using images from an external source, configure domains in next.config.js:

   module.exports = {
     images: {
       domains: ['example.com'],
     },
   };

Wrapping Up

By using the Next.js Image component and following these best practices, you’ll ensure smooth loading, a stable layout, and a more professional website experience.

• 📏 Specify dimensions
• 🔄 Use blur placeholders and lazy loading
• 📈 Monitor your CLS scores

Enjoy coding with Next.js, and let your images load proficiently! 🎉