Rocket Loader priorities your website’s content (text, images, fonts, etc) by deferring all of your JavaScript loadings until after rendering. 

On pages with JavaScript, this results in a much faster loading experience for your users and improves the following performance metrics:

• Time to First Paint (TTFP)
•  Contentful Paint (TTFCP)
•  Meaningful Paint (TTFMP)
• Document Load

To learn more about the latest version of Rocket Loader visit the blog: Cloudflare

Addition optional configuration:

• If you have a Content Security Policy, you will need to update it.

It is to allow Rocket Loader to run: What is Content Security Policy (CSP), and how can I use it with Cloudflare?

• If you have specific scripts you want to not optimize, you can do this by modifying your HTML script tags. How can I have Rocket Loader ignore specific JavaScripts?