vue-li-image

A Vue.js component to lazy load an image automatically when it enters the viewport using the Intersection Observer API.

This is an opinionated upgrade of the original Vue Lazy Image loading library v-lazy-image including certain fixes already submitted as pull requests on the original library, which were never merged. Kudos to Alex Jover for the original idea!

Usage

 npm install vue-li-image

Warning: You'll need to install the w3c Intersection Observer polyfill in case you're targeting a browser which doesn't support it.

You can register the component globally so it's available in all your apps:

 import Vue from "vue";
import { VueLiPlugin } from "vue-li-image";

Vue.use(VueLiPlugin);

Or use it locally in any of your components:

 import VueLi from "vue-li-image";

export default {
  components: {
    VueLi
  }
};

You must pass an src property with the link of the image:

 <template>
  <vue-li src="http://lorempixel.com/400/200/" />
</template>

That image will be loaded as soon as the image enters the viewport.

Progressive Loading

You can use the src-placeholder property to define an image that is shown until the src image is loaded.

When the src image is loaded, a vue-li-loaded class is added, so you can use it to perform animations. For example, a blur effect:

 <template>
  <vue-li
    src="https://cdn-images-1.medium.com/max/1600/1*xjGrvQSXvj72W4zD6IWzfg.jpeg"
    src-placeholder="https://cdn-images-1.medium.com/max/80/1*xjGrvQSXvj72W4zD6IWzfg.jpeg"
  />
</template>

<style scoped>
.vue-li {
  filter: blur(10px);
  transition: filter 0.7s;
}
.vue-li {
  filter: blur(0);
}
</style>

In case you are using Webpack bundler for images too (just like Vue-cli):

 <vue-li
  src="https://cdn-images-1.medium.com/max/1600/1*xjGrvQSXvj72W4zD6IWzfg.jpeg"
  :src-placeholder="require('../assets/img.jpg')"
/>

You could listen to the intersect and load events for more complex animations and state handling:

 <template>
  <vue-li
    src="https://cdn-images-1.medium.com/max/1600/1*xjGrvQSXvj72W4zD6IWzfg.jpeg"
    src-placeholder="https://cdn-images-1.medium.com/max/80/1*xjGrvQSXvj72W4zD6IWzfg.jpeg"
    @intersect="..."
    @load="..."
  />
</template>

@jmperezperez has written about the progressive loading technique on his blog, in case you want a deeper explanation.

Responsive Images

Using the srcset property you can set images for different resolutions:

 <template>
  <vue-li
    srcset="image.jpg 1x, image_2x.jpg 2x"
  />
</template>

When using the srcset attribute is recommended to use also src as a fallback for browsers that don't support the srcset and sizes attributes:

 <template>
  <vue-li
    srcset="image-320w.jpg 320w, image-480w.jpg 480w"
    sizes="(max-width: 320px) 280px, 440px"
    src="image-480w.jpg"
  />
</template>

The srcset prop is combinable with src-placeholder in order to apply progressive loading.

Picture

If you want to wrap the img in a picture tag, use the prop usePicture. You can then use slots to add additional elements above the img element`.

 <vue-li
  srcset="image-320w.jpg 320w, image-480w.jpg 480w"
  alt="Fallback"
  use-picture
>
  <source srcset="image-320w.jpg 320w, image-480w.jpg 480w" />
</vue-li>

Renders as:

 <picture>
  <source srcset="image-320w.jpg 320w, image-480w.jpg 480w" />
  <img srcset="image-320w.jpg 320w, image-480w.jpg 480w" alt="Fallback" />
</picture>

Note you can use the picture polyfill.

API

Aside from the following API, you can pass any img attribute, such as alt, and they'll be added to the rendered <img> tag.

Fields marked as (*) are required.

Props

Name	Type	Default	Description
src	String (*)	-	Image src to lazy load when it intersects with the viewport
src-placeholder	String	' '	If defined, it will be shown until the src image is loaded. Useful for progressive image loading, see demo
src-fallback	String	' '	If defined, it will be shown if the src image fails to load
srcset	String	-	Images to be used for different resolutions
intersection-options	Object	() => ({})	The Intersection Observer options object.
use-picture	Boolean	false	Wrap the img in a picture tag.

Events

Name	Description
intersect	Triggered when the image intersects the viewport
load	Triggered when the lazy image defined in src is loaded
error	Triggered when the lazy image defined in src fails to load