AskTaimoor

All this plugin does is that it adds ‘async’ in all script tags it find on the page. 
This helps in loading the webpage much faster.

Async Javascript Optimizer

Adds async to all javascript links for fast loading of webpage.

FanaticPythoner

Dynamic Shortcode is a 100% FREE plugin that allows users to make any shortcode asynchronous in one simple step, meaning it won’t block the WordPress page render at all. Dynamic Shortcode has a simple and user friendly interface, making it extremely easy to use.

Dynamic Shortcode can either replace every occurence of a given shortcode without your intervention (currently in beta, the feature is called Dynamic Replace), or you can change every shortcode yourself in one simple step:

<ul>
<li>Find an occurence of your shortcode, and replace your shortcode’s name with wp_dynamic and add a parameter named shortcode with your shortcode’s name as a value. For example:
[myShortcode] becomes
[wp_dynamic shortcode=”myShortcode”] 
</li>
</ul>
But wait! That’s not all: You can even add custom placeholders for each individual shortcode. Placeholders are displayed when Dynamic Shortcode is loading a shortcode asynchronously.

Dynamic Shortcode is packed with tons of other useful features.

For each individual shortcode on your site, here’s everything Dynamic Shortcode can do for you:
<ul>
<li>
Make any already existing shortcode asynchronous automatically or in a single step
</li>
<li>
Add custom placeholders for when your Dynamic Shortcode is loading your shortcode
</li>
<li>
Run a validation function before executing your shortcode when making the asynchronous call
</li>
<li>
Choose which GET parameters to ignore when doing the asynchronous call
</li>
<li>
Choose which POST parameters to ignore when doing the asynchronous call
</li>
<li>
Choose which shortcode attribute to ignore when doing the asynchronous call
</li>
</ul>

Dynamic Shortcode

Make any shortcode asynchronous - Eliminate render-blocking shortcodes, improve user experience and Google PageSpeed Insights.

Async Javascript Optimizer vs Dynamic Shortcode