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Package contao-speed-bundle
Short Description This module improves the performance of your contao environment.
License LGPL-3.0-or-later
Informations about the package contao-speed-bundle
Contao speed bundle
This module improves the performance of your contao environment.
Improvements
Lazy-loading offscreen images
Offscreen images are images that appear below the fold. Since users can't see offscreen images when they load a page, there's no reason to download the offscreen images as part of the initial page load. In other words, deferring the load of offscreen images can speed up page load time and time to interactive.
We ship an adjusted picture_lazyload.html5
with this bundle to provide proper lazy loading setup for images (picture_default.html5
will be replaced with picture_lazyload.html5
if script js_lazyload
in tl_layout.scripts
is enabled). If in case you use custom picture-*.html5
templates adjust like the following:
How to use?
To enable lazy loading, enable the js_lazyload
JavaScript-Template within your page layout.
Background images
We also support lazy loading for background images. To take advantage of this feature, add the css class lazy
to the background image container and provide the path to the image within the data-src
attribute.
Lazy load inside sliders like slick slider
In order to prevent bouncing of cloned carousel slide images (using infinite looping), the lazyLoad
technique should be set to progressive
instead of on-demand
.
Prevent lazy loading
If you want to prevent your image from being lazy loaded, you have to adjust your template and add ['lazyload' => false]
to the picture template data.
Example: ce_image.html5
If you use the heimrichhannot/contao-utils-bundle
TwigExtension image
, just add 'lazyload': false
to your item data.
Update lazy load on demand
If you need to update your lazy load instances on demand, for example using the barba.js PJAX page transition plugin, use the window.lazyLoad.update()
function.
Callbacks
In order to make adjustments like trigger animation on scroll after image has been loaded, there are some callbacks you might listen on the image:
Name | Meaning | Example |
---|---|---|
lazyload:enter |
A function which is called when an element enters the viewport. | document.querySelector('[data-lazy]').addEventListener('lazyload:enter', function(event){}); |
lazyload:set |
A function which is called after the src /srcset of an element is set in the DOM. |
document.querySelector('[data-lazy]').addEventListener('lazyload:set', function(event){}); |
lazyload:load |
A function which is called when an element was loaded. | document.querySelector('[data-lazy]').addEventListener('lazyload:load', function(event){}); |
😋 Tips & tricks
Do NOT use placeholder images
Taken from the verlok/lazyload
github README.md:
We do not recommend to use a placeholder image (like a transparent pixel GIF) in your HTML.
- For best perceived performance, leave the
src
andsrcset
attributes blank. Doing so, the image will be shown as soon as LazyLoad starts loading the image. See this video or [this pen](https://> codepen.io/verlok/pen/bKYggE?editors=0110) to test the difference (remember to disable the cache and to set a slower connection speed if you have a very fast one).- If you put anything in the src (like a transparent GIF), then LazyLoad starts loading the image but it won't be shown by browsers until the new image is loaded, leading to a worse perceived performance.
It's safe not to put any value in the
src
norsrcset
attributes, even if your HTML won't validate by a static code analyzer. The reason is that once JavaScript is executed, those values will be set by LazyLoad. For SEO, if the > client is a crawler like Googlebot, it will be detected by LazyLoad which will fix the HTML.