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:
- Page text loads.
- Image starts downloading.
- 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}
loading="lazy"
/>
);
}
🗝️ Key Features That Prevent Layout Shift
Reserved Space for Smooth Loading
Required Dimensions
With the Image component,width
andheight
properties are mandatory. This reserves space for the image even before it loads, preventing layout shifts.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.
- 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" />
- 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" />
-
Set Priority for Critical Images
For hero images or other important visuals, set the
priority
property totrue
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 ⚠️
- 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" />
-
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! 🎉
Top comments (3)
Nice Explanation. thank you
Thanks for the screenshot and great article.
Tips on priority
•If the image in ProductCard is above the fold and immediately visible when the page loads, set priority={true}.
•If it requires scrolling to become visible, then keep priority={false} or omit the prop.
Also
If you use priority={true}, you don’t need to set loading="lazy" because it won’t make a difference.
If you use priority={false}, then loading="lazy" is a good option for below-the-fold images to ensure they load only when needed.
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