Image Lazy Loading

Lazy loading has been a term that was hot about 15 years ago and never stopped being in fashion. The images are mostly the heaviest part of a website and tend to slow everything down.

It was always pretty tedious to make a custom JavaScript for lazy loading, but we now have the native lazy loading API!

It can be as simple as adding loading="lazy" to an image element.

HTML Structure

<img
  src="https://images.unsplash.com/photo-1591303872989-2640dc28185b?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=3236&q=80"
  loading="lazy"
  onload="alert('Cool right!');"
/>

We can define the loading attribute and give it the value of lazy, and the API comes with an onload callback function.

Other values we can use are:

auto - Default behavior, browser-specific
lazy - Loads the image when it becomes visible based on scroll
eager - Loads the image directly

See this in action on the following Codepen.

See the Pen Image Lazy Loading by Chris Bongers (@rebelchris) on CodePen.

Browser Support

Unfortunately, it’s not fully supported by all browsers, but keep in mind if the browser doesn’t support it, it will just show the image, so there is no harm in adding this!