Lazyload Images Responsively
This package was inspired by https://github.com/ivopetkov/responsively-lazy/. It uses very similar markup, but significantly simplifies the way image replacement is handled under the hood. It also adds an optional fallback for when JavaScript is disabled.
Quick Start
Check out the examples for copy-pasteable code and more information about usage.
Option 1: Using a Build Tool
This example assumes webpack.
1. Install the module using npm.
npm install --save responsive-lazyload2. Include the module and initialize lazyloading.
Load the module and initialize lazyloading in your app's script:
; ;3. Include the stylesheet.
Include the following in the <head> of your document.
4. Add a lazyloaded image to your markup.
Place the lazyload markup anywhere in your app's markup:
For more information and configuration options, see the examples.
Option 2: Using unpkg
NOTE: While unpkg is a fantastic tool, adding additional HTTP requests to your project will slow it down. For that reason, this approach is not recommended.
1. Include the script in your markup.
Just before the closing </body> tag, add the lazyloading script:
2. Include the styles in your markup.
Include the following in the <head> of your document:
3. Initialize lazyloading.
The initialization function is stored inside a global object called responsiveLazyload. Initialize lazyloading by adding the following just below the script include:
4. Add a lazyloaded image to your markup.
Place the lazyload markup anywhere in your app's markup:
For more information and configuration options, see the examples.
Markup
The markup to implement this is:
Markup Details
- The classes can be changed, but must be updated in the call to
responsiveLazyload(). - The initial
srcsetis a blank GIF, which avoids an unnecessary HTTP request. - The actual
srcsetis added asdata-lazyload.
The way responsiveLazyload() works is to check if the image is inside the viewport, and — if so — swap out the srcset for the data-lazyload. This is much simpler than duplicating browser behavior to choose the optimal image size; instead, we just give the browser a srcset and let it do its thing.
On browsers that don’t support srcset, the regular src attribute is used, so this should degrade gracefully.
Markup With Fallback for Browsers Without JavaScript Enabled
To ensure that an image is still visible, even if JavaScript is disabled, add a <noscript> block with the properly marked up image using srcset without the lazyloading solution:
JavaScript Options
To enable lazyloading, add the following to your initialization script:
; ;| option | default | description |
|---|---|---|
containerClass |
js--lazyload |
Determines which elements are targeted for lazyloading. |
loadingClass |
js--lazyload--loading |
Applied to containers before loading. This is useful for adding loading animations. |
callback |
() => {} |
Fired on each image load. Useful for adding custom functionality after an image has loaded. |
Development
To run this module locally for development, follow these steps:
# Clone the repo. git clone git@github.com:jlengstorf/responsive-lazyload.js.git # Move into the repo. cd responsive-lazyload.js/ # Install dependencies. npm install # Run the build script. npm run buildTesting
Tests are built using Jest. Run them with:
npm test # Or, to remove all the extra crap npm spits out and only show test output: npm test --silent