With WordPress lazy load plugins your website serve content only when it is visible to the visitor. The lazy load technique is opposite of what is known as content preloading. It is quite popular and used on many high traffic websites to lower bandwidth usage and to ensure the visible elements are served first, check out huffingtonpost.com to see the effect. It is great for user experience and stable operations. Lazy loading content often applies to images, but recently it has become very popular to integrate interactive social media buttons everywhere and they are potential performance killers!
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BJ Laazy Load replaces all your post images, post thumbnails, gravatar images and content iframes with a placeholder and loads the content as it gets close to enter the browser window when the visitor scrolls the page. It uses jQuery and degrades gracefully for non-js users. It works with both images and iframes. You are able to control what content elements to lazy load and where the script is inserted. This is quite nice.
WordPress Advanced Image Lazy Load (premium plugin)
Please note that some themes that are based on an advanced framework may use an image preload mechanism that may break the lazy loading script. There is a lot of options and settings available on this plugin. You can control what posts and page the script applies to and if it should be used on mobile devices etc.
This plugin gives you lazy load of images to improve page load times. It uses jQuery.sonar to only load an image when it’s visible in the viewport. There is no options or setting to make, once the plugin is activated your images will load only when visible.
Another really simple and no options available lazy loader plugin for WordPress. It is based on the Lazy Load jQuery plugin and may seem outdated at first. However it works great on recent versions of WordPress.
Lazy Widget Loader provides lazy loading for widgets to improve page loading. It is useful for holding back slow widgets e.g. with content from external sources like Facebook, Twitter and AdSense.
WP YouTube Lyte allows you to “lazy load” your video’s, by inserting “Lite YouTube Embeds”. These look and feel like normal embedded YouTube, but only call the actual “fat” Flash or HTML5-player when clicked on, thereby reducing download size & rendering time substantially when embedding YouTube occasionally and improving page performance dramatically when you’ve got multiple YouTube video’s on one and the same page.
MooTools Image Lazy Load (Tested: and I’m not sure it worked on my demo WordPress 3.4.2)
This plugin adds lazy loading to WP images and use the Mootools Lazy Load plugin, however I was not able to see the lazy loading as with all the plugins above that I tested.
Ai Loader (Tested: and did not work on my demo WordPress 3.4.2)
Once I activated this plugin was not able to save blog posts due to a runtime error!