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2.1.8 • Public • Published

💤 Novicell Lazyload

Image lazyloading script in vanilla javascript

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Written in pure Vanilla JS, depends on lazysizes and some kind of serverside image processor as the It ships with examples for easy implementation with the novicell-frontend setup.

Install with npm

npm install novicell-lazyload@next --save

Or simply:

npm i novicell-lazyload@next


Import novicell-lazyload as a module in your javascript file that observes the images. Also add debounce from lodash.

import NovicellLazyLoad from 'novicell-lazyload';
import debounce from 'lodash/debounce';
const lazy = new NovicellLazyLoad({
    includeWebp: true // optional  
document.addEventListener('lazybeforeunveil', function(event) {
}, true);
window.addEventListener('resize', function() {
}, 100, false);


includeWebp: true/false Default true. Optional, but if it's set to true, Novicell-lazyload will still check if the client's browser supports WebP first.


window.lazySizesConfig = {
    useWebp: true // Boolean (defaults to true). If true is used it will still check if browser supports WebP format and then add it


This script lazyloads by swapping the data-src or data-srcset to an actual src or srcset. For all implementations you should have a lazyload-class and data-query-obj on the image. Everything inside the data-query-obj is general settings that is applied on every src in the srcset as a querystring".

For extra plugins and complete feature list, please reference the lazysizes documentation.

Images with fixed sizes (lazyload)

For images with fixed sizes we recommend using a specific srcset, as this is the fastest.

<img class="lazyload" data-src="/dist/images/test.jpg" alt="Cool image" data-query-obj='{"mode":"crop", "quality":"70", "center": "0.8,0.3"}'
data-srcset="/dist/images/test.jpg?width=1500&heightratio=0.6 1000w,
             /dist/images/test.jpg?width=900&heightratio=0.6 800w,
             /dist/images/test.jpg?width=400&heightratio=1 500w"/>

Images with variable sizes (lazyload-measure)

For images with variable sizes, eg. a full width banner with a fixed height, or just an image added in the CMS inside a random grid column, we recommend the "measure"-feature.

This feature will get the size of the parent element, and add it as query strings for this image.

<img class="lazyload lazyload-measure" data-src="/dist/images/test.jpg" alt="Cool image" data-query-obj='{"mode":"crop", "quality":"70", "center": "0.8,0.3"}'/>

Using height ratio (or auto height)

If you just want auto height you can add the attribute ´data-height-ratio="0"´ You can also pass a height-ratio, this will set the size accordingly.

Useful height ratios: 0: Auto height 0.5: Half height as width 0.5625: 16:9 format 0.625: 16:10 format 1: Square image 2: Twice height as width

<img class="lazyload lazyload-measure" data-src="/dist/images/test.jpg" alt="Cool image" data-height-ratio="0" data-query-obj='{"mode":"crop", "quality":"70", "center": "0.8,0.3"}' />

Background images (lazyload-bg)

This uses the "measure"-feature only adding the image as a background image on the parent element, instead of an actual <img>-tag.

<img class="lazyload lazyload-measure lazyload-bg" data-src="/dist/images/test.jpg" alt="Cool image" data-query-obj='{"mode":"crop", "quality":"70", "center": "0.8,0.3"}'/>


For extending the component please reference the Novicell wiki page 🕮.


npm i novicell-lazyload

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