To eliminate JavaScript render-blocking, you add the async or defer attributes to the <script> tag. However, this can affect the order in which the scripts load so if there are dependencies on the scripts then the scripts can break. JCH Optimize does this in a safe way to preserve dependency when you use the Optimum setting in the Combine Files Automatic Settings section on The Dashboard . This enables the Defer/Async JavaScript setting on the JavaScript tab on The Options Page .

The Optimum setting defers or loads JavaScript asynchronously

With the Optimum setting enabled, if there is only one combined file, the file is placed at the bottom of the HTML just before the </body> tag and the async attribute is added to the <script> tag. If there are more than one files then the defer attribute is used instead on each of the files at the bottom of the page. If a script was excluded while maintaining the original execution order of files on the page, then only the combined files falling below the excluded scripts will be deferred. This ensures that the dependencies of the files are maintained.

	Important
	Please note that excluded files and combined files above the excluded files will not be deferred.

Dynamically loaded files cannot be deferred.  If you're not excluding files and using the Optimum setting but still seeing this alert being triggered on PageSpeed then this is likely caused by files that are being loaded dynamically using JavaScript. This means the links to these files are not embedded in the HTML so the plugin cannot access these files to optimize and combine them.

To confirm, check the HTML source for the links of the files that are triggering this error. If they are not in the source then it means they were loaded dynamically. You may want to consider keeping these files off your landing pages to the best extent possible. Google apps and social media applications are notorious for this.