# Lozad.js [![npm version](https://badge.fury.io/js/lozad.svg)](https://badge.fury.io/js/lozad) [![Build Status](https://travis-ci.org/ApoorvSaxena/lozad.js.svg?branch=master)](https://travis-ci.org/ApoorvSaxena/lozad.js) [![npm](https://img.shields.io/npm/dm/lozad)](https://www.npmjs.com/package/lozad) [![](https://data.jsdelivr.com/v1/package/npm/lozad/badge)](https://www.jsdelivr.com/package/npm/lozad) > Highly performant, light and configurable lazy loader in pure JS with no dependencies for images, iframes and more, using IntersectionObserver API ![lozad.js lazy loading javascript library](./banner/lozad-banner.jpg "lozad.js lazy loading javascript library") **Lozad.js**: - lazy loads elements performantly using pure JavaScript, - is a light-weight library, just [![](http://img.badgesize.io/https://cdn.jsdelivr.net/npm/lozad?compression=gzip)](https://cdn.jsdelivr.net/npm/lozad) minified & gzipped, - has NO DEPENDENCIES :) - allows lazy loading of dynamically added elements as well, - supports <img>, <picture>, iframes, videos, audios, responsive images, background images and multiple background images etc. - even supports LQIP (Low Quality Image Placeholder) - is completely free and open source. It is written with an aim to lazy load images, iframes, ads, videos or any other element using the recently added [Intersection Observer API](https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API) with tremendous performance benefits. ## Featured in: - [Web | Google Developers](https://developers.google.com/web/fundamentals/performance/lazy-loading-guidance/images-and-video/) - [Product Hunt](https://www.producthunt.com/posts/lozad-js) - [Reddit](https://www.reddit.com/r/webdev/comments/6zg1x0/highly_performant_light_05kb_and_configurable/) - [CSS Tricks](https://css-tricks.com/lozad-js-performant-lazy-loading-images) - [David Walsh](https://twitter.com/davidwalshblog/status/915319510646829061) - [Codrops](https://twitter.com/Apoorv_Saxena/status/906586828265758720) - [SitePoint](https://www.sitepoint.com/five-techniques-lazy-load-images-website-performance/) ## Brands using Lozad.js: ![Tesla](./brands/tesla.png) ![Binance](./brands/binance.png) ![Domino's](./brands/dominos.png) ![BNP Paribas](./brands/bnp-paribas.png) ![Mi](./brands/xiaomi.png) ![Amway](./brands/amway.png) ![TATA](./brands/tata.png) ![Verizon](./brands/verizon.svg) ![Atlassian](./brands/atlassian.svg) ![BNP Paribas](./brands/livemint.svg) ![JLM Couture](./brands/jlm-couture.png) ![New Balance](./brands/new-balance.png) ![BBC](./brands/bbc.png) and many more... ## Table of Contents - [Demo](https://apoorv.pro/lozad.js/demo/) - [Background](#yet-another-lazy-loading-javascript-library-why) - [Install](#install) - [Usage](#usage) - [Example with picture tag](#example-with-picture-tag) - [Browser Support](#browser-support) - [FAQs](#faqs) - [Contribute](#contribute) - [Changelog](#changelog) - [License](#license) ## Yet another Lazy Loading JavaScript library, why? Existing lazy loading libraries hook up to the scroll event or use a periodic timer and call `getBoundingClientRect()` on elements that need to be lazy loaded. This approach, however, is painfully slow as each call to `getBoundingClientRect()` forces the browser to re-layout the entire page and will introduce considerable jank to your website. Making this more efficient and performant is what [IntersectionObserver](https://developers.google.com/web/updates/2016/04/intersectionobserver) is designed for, and it’s landed in Chrome 51. IntersectionObservers let you know when an observed element enters or exits the browser’s viewport. ## Install ```sh # You can install lozad with npm $ npm install --save lozad # Alternatively you can use Yarn $ yarn add lozad # Another option is to use Bower $ bower install lozad ``` Then with a module bundler like rollup or webpack, use as you would anything else: ```javascript // using ES6 modules import lozad from 'lozad' // using CommonJS modules var lozad = require('lozad') ``` Or load via **CDN** and include in the `head` tag of your page. ```html ``` When loading from CDN, you can find the library on `window.lozad`. ---

## Usage In HTML, add an identifier to the element (default selector identified is `lozad` class): ```html

``` All you need to do now is just instantiate Lozad as follows: ```js const observer = lozad(); // lazy loads elements with default selector as '.lozad' observer.observe(); ``` or with a DOM `Element` reference: ```js const el = document.querySelector('img'); const observer = lozad(el); // passing a `NodeList` (e.g. `document.querySelectorAll()`) is also valid observer.observe(); ``` or with custom options: ```js const observer = lozad('.lozad', { rootMargin: '10px 0px', // syntax similar to that of CSS Margin threshold: 0.1 // ratio of element convergence }); observer.observe(); ``` Reference: - [IntersectionObserver options: rootMargin](https://developer.mozilla.org/en-US/docs/Web/API/IntersectionObserver/rootMargin) - [IntersectionObserver options: thresholds](https://developer.mozilla.org/en-US/docs/Web/API/IntersectionObserver/thresholds) or if you want to give custom function definition to load element: ```js lozad('.lozad', { load: function(el) { console.log('loading element'); // Custom implementation to load an element // e.g. el.src = el.getAttribute('data-src'); } }); ``` If you would like to extend the `loaded` state of elements, you can add the loaded option: > **Note**: The `"data-loaded"="true"` attribute is used by lozad to determine if an element has been previously loaded. ```js lozad('.lozad', { loaded: function(el) { // Custom implementation on a loaded element el.classList.add('loaded'); } }); ``` If you want to lazy load dynamically added elements: ```js const observer = lozad(); observer.observe(); // ... code to dynamically add elements observer.observe(); // observes newly added elements as well ``` for use with responsive images ```html

``` for use with background images ```html

``` for use with multiple background images ```html

``` for use with responsive background images (image-set) ```html

``` To change the delimiter that splits background images: ```html

``` If you want to load the images before they appear: ```js const observer = lozad(); observer.observe(); const coolImage = document.querySelector('.image-to-load-first') // ... trigger the load of a image before it appears on the viewport observer.triggerLoad(coolImage); ``` ### Large image improvment Sometimes image loading takes a long time. For this case, you can add a placeholder background: ```html

``` Lozad sets a placeholder background color of img element and users will see the fallback till the image loads. ## Example with picture tag Create _a broken_ picture element structure. > IE browser don't support picture tag! > You need to set `data-iesrc` attribute (only for your picture tags) with source for IE browser > `data-alt` attribute can be added to picture tag for use in `alt` attribute of lazy-loaded images ```html ``` When _lozad_ loads this picture element, it will fix it. If you want to use image placeholder (like low quality image placeholder), you can set a temporary `img` tag inside your `picture` tag. It will be removed when _lozad_ loads the picture element. ```html

``` ## Example with video ```html

``` ## Example with iframe ```html ``` That's all, just add the `lozad` class. ## Example toggling class ```html

``` The `active` class will be toggled on the element when it enters the browser’s viewport. ## Browser Support Available in [latest browsers](http://caniuse.com/#feat=intersectionobserver). If browser support is not available, then make use of [polyfill](https://www.npmjs.com/package/intersection-observer). For IE11 support, please make use of these [polyfills](https://polyfill.io/v3/polyfill.min.js?flags=gated&features=Object.assign%2CIntersectionObserver). ## FAQs Checkout the [FAQ Wiki](https://github.com/ApoorvSaxena/lozad.js/wiki/Frequently-Asked-Questions) for some common gotchas to be aware of while using **lozad.js** ## Contribute Interested in contributing features and fixes? [Read more on contributing](./CONTRIBUTING.md). ## Changelog See the [Changelog](https://github.com/ApoorvSaxena/lozad.js/wiki/Changelog) ## License [MIT](LICENSE) © [Apoorv Saxena](https://apoorv.pro)

	Stars	Issues	Version	Updated	Created
lazyload			2.0.0-rc.2	5 years ago	11 years ago
lozad	7,413	71	1.16.0	4 years ago	7 years ago
react-lazy-load	975	20	4.0.1	2 years ago	9 years ago
react-measure	1,938	31	2.5.2	4 years ago	9 years ago

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