Brian Zeligson

<p>This plugin uses the wp_print_scripts action hook, as opposed to output buffering and regex used by alternative implementations.</p>
<p>The downside of this method is that only scripts loaded via wp_enqueue_script will be affected by the plugin, the upside is better<br />
performance by avoiding output buffering on every page load.</p>
<p>The plugin will preserve any localizations added via wp_localize_script, and uses the first parameter passed to wp_enqueue_script<br />
as the label for the script in the head.js call. For example,</p>
<pre><code>wp_enqueue_script('jquery', 'https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js');
</code></pre>
<p>would show up as</p>
<pre><code>head.js({"jquery": "https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"});
</code></pre>
<p>This allows you to run callbacks when specific scripts are ready, such as</p>
<pre><code>head.ready('jquery', function() {
    //do something when jquery is loaded
});
</code></pre>
<p>For more on HeadJS usage, see http://headjs.com/</p>


WP HeadJS

Uses HeadJS to load your enqueued scripts asynchronously, in parallel, executing them in order.

dmikam

<p>When your page is loaded by browser – all that stuff placed in HEAD tag is loaded before the page content – in blocking way. So the content is delivered to user in the last moment, after all javascript and css files are loaded.</p>
<p>If you are a webmaster or just want to make your web to make better your positions on search engines (yes, they preffer faster webs), just take a look on Google PageSpeed Insights – you’ll see that one of the mos important things is fastenes and one of the reason why your page is not so fast – is “Render-blocking JavaScript and CSS”.</p>
<p>This plugin makes ALL scripts loaded by other plugins to be loaded in asynchronous way just like Google PageSpeed Insights recommends.<br />
All CSS files will be inserted inline into the document code or moved from the document beginning to the end, just before closing BODY tag (or just where you placed wp_foot() function). There are various methods to do that – they are all in plugin’s configuration page.</p>
<p>Plugin makes all scripts to be loaded asynchronously using wp_enqueue_script and also can detect scrips included inside of wp_head and wp_footer hooks.</p>
<p>All CSS files loaded using wp_enqueue_style can be loaded just before closing BODY tag by four methods:</p>
<pre><code>* inserting <link rel="stylesheet" ...> tag

* inserting <style>@import url(...);</style>

* generating <link rel="stylesheet" ...> tag with javascript after all have loaded

* inserting ALL CSS CODE INLINE into the document (the fastest way)
</code></pre>
<p>I was inspired to create this small plugin by Asynchronous Javascript but it works in completely different way.</p>
<h3>Known incompatibilities</h3>
<pre><code>* Internet Explorer 7 - Some scripts could be loaded impropertly (trying to fix it)

* Plugin - WP JetPack - Share - everithing works but "More" dropdown menú

* Plugin - Google Analyticator<h3>Special thanks</h3>
* NicMic<h3>TODO</h3>
* Inline JS
* Minify JS
* Cache
</code></pre>


Async JS and CSS

Very good plugin in a sense that we could optimize at least something and exclude css and js that couldn't be touched.



Finally plugin that works for us

Does the job and helps to do more tweaks. 

Very good plugin

Converts render-blocking CSS and JS files into NON-render-blocking, improving performance of web page.

WP HeadJS vs Async JS and CSS