simply-lazy

Simply Lazy

A simple, lightweight (0.6kb), pure JavaScript image lazy loader that even works in IE* utilizing the IntersectionObserver API.

See the Browser Support section for more information regarding browser support.

DEMO

View the live demo here. This GitHub pages demo is hosted in this repository's /docs directory for you to see exactly how it is used.

Quick Setup Guide

Lazy loading doesn't have to be complicated. It's as simple as these 3 steps:

1. Add the script:

<script type="text/javascript" src="./simplyLazy.min.js"></script>

1. Setting your images up with a data-src attribute:

<img data-src="/path/to/img.jpg" />

1. Initialize the lazy loader:

SimplyLazy(optionalOptions).lazy(selector)

Additionally there is an options object you can use to get callbacks or set default information.

Callbacks

Function	Description
onImageLoad(imgEl)	Called after an image loads and it will receive the imageElement as a parameter
onImageError(imgEl)	Called if there is an error loading the image (i.e. 404), it will receive the imageElement as a parameter

Parameters

Parameter	Type	Values	Default
defaultImage	String	path to default image or base64 string	null

defaultImage is only called onImageError and if it has a value. This can be useful if there is an error loading an image like a 404 but you still want to show a default placeholder image. The value you use for defaultImage will be set to the src of the <img> element. The example below is a base64 string of an empty image placeholder.

Here is an example usage with all of the options:

SimplyLazy({
  onImageLoad: (imgEl) => {
    // Called after an image loads
  },
  onImageError: (imgEl) => {
    // Called if there is an error loading the image
  },
  defaultImage: 'data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==' // An empty image, can be replaced with a known image URL
}).lazy(selector);

The selector can be any selector you would typically use when using el.querySelectorAll, like a class name.

In your HTML you only need to set a data-src equal to your image src. Note: Do not set the src or else you will override this plugin!

<img data-src"/path/to/img.jpg" />

Browser Support

This is supported in all major browsers and will even work in IE with one simple tweak.

For IE to work you must add this Polyfill script to your app which will only be loaded in browsers that do not support IntersectionObserver (like IE). All other browsers will not load anything when using this script from Polyfill.io:

<script src="https://polyfill.io/v3/polyfill.min.js?features=IntersectionObserver"></script>

Contributions

Contributions are always welcome. Please fork this repo and submit a PR.

Create an issue here.

Contributors

Max Poshusta