How to avoid Image warnings with NextJS

When using the Image component in Next.js, you may encounter certain warnings, particularly related to image optimization and loading performance. Below, I'll cover several common warnings and how to avoid them:

1. Using Correct Image Dimensions

Warning example: Image with src "/url/to/image.jpg" has a "width" of 500px but was not provided a "height" attribute.

The Image component in Next.js utilizes built-in image optimization techniques. To maximize the effectiveness of these optimizations, you must provide the correct width and height attributes for the Image component. These attributes not only help Next.js anticipate the image size but also prevent layout shifts, thereby enhancing user experience.

Solution:

Ensure you provide appropriate width and height attributes when using the Image component. For example:

jsx
import Image from 'next/image'

export default function MyImage() {
  return (
    <Image
      src="/url/to/image.jpg"
      width={500}
      height={300}
      alt="Description"
    />
  )
}

2. Using Appropriate Loading Strategies

Warning example: Image elements do not have explicit width and height

Next.js offers various loading strategies, such as lazy loading (the default behavior). For images outside the viewport, lazy loading defers loading these images, improving page load time and performance.

Solution:

First, ensure explicit dimensions are set for each image. Second, choose the appropriate loading strategy as needed:

jsx
<Image
  src="/url/to/image.jpg"
  width={500}
  height={300}
  alt="Description"
  loading="eager" // or "lazy" (default)
/>

3. Optimizing Image Resources

Warning example: The provided image does not have srcset attributes

To further optimize images, Next.js recommends using modern formats like WebP, which typically offer better compression rates compared to traditional formats such as JPEG or PNG.

Solution:

Ensure your server or image service supports automatic format conversion, and leverage the Image component's optimization capabilities when possible:

jsx
<Image
  src="/url/to/image.jpg"
  width={500}
  height={300}
  alt="Description"
  quality={75}
  formats={['image/avif', 'image/webp']}
/>

The above methods help avoid common warnings when using the Image component in Next.js. By following these best practices, you can not only improve web performance but also deliver a smoother user experience.