add lazy loading to WP, more info at http://plugins.jquery.com/project/lazyload

jQuery Image Lazy Load WP

Willy Bahuaud

Grégory Viguier

Daniel Roch

This plugin defer the loading of all JavaScripts added by the way of <code>wp_enqueue_script()</code>, using LABJS. The result is a significant optimization of loading time.
It is compatible with all WordPress JavaScript functions (<code>wp_localize_script()</code>, js in header, in footer…) and works with all well coded plugins.
If a plugin or a theme is not properly enqueuing scripts, your site may not work. Check this page: <a href="https://codex.wordpress.org/Function_Reference/wp_enqueue_script" rel="nofollow ugc">Function Reference/wp_enqueue_script on WordPress Codex</a>.
LABjs (Loading And Blocking JavaScript) is an open-source (MIT license) project supported by <a href="http://getify.com/" rel="nofollow ugc">Getify Solutions</a>.
We performed a range of tests to determine the potential benefit of loading time. On <a href="http://wabeo.fr" rel="nofollow ugc">wabeo</a> we executed <a href="http://webwait.com/" rel="nofollow ugc">webwait</a> (150 calls by test). Result is this plugin could improve your loading time by 25%!! 
More information in the <a href="https://wordpress.org/extend/plugins/wp-deferred-javascripts/screenshots/" rel="ugc">Screenshots section</a>.
You can find <a href="http://www.seomix.fr/wp-deferred-javascript/" rel="nofollow ugc">more information about WP Deferred JavaScripts</a> and <a href="http://wabeo.fr/blog/wordpress-javascripts-asynchrones/" rel="nofollow ugc">technical information about asynchronous scripts</a> on authors blogs.

WP Deferred JavaScripts

For instance breaks Ajax in Contact 7. To avoid IMO.

Can break other stuff, hard to trace back

Great! Easy to use if you need to fine tune speed of your web.

There is a need to spped up web downloading, after cache you can use this to optimize Javascript download. But it needs fine tuning otherwise you will get some strange results like pages that do not render properly for a few seconds. Always begin by using a cache plugin. 

Great! Use if you need to fine tune speed of your website

Defer the loading of all JavaScripts added with wp_enqueue_script(), using LABJS (an asynchronous javascript library).

jQuery Image Lazy Load WP vs WP Deferred JavaScripts