Minimize main thread work

The browser’s main thread processes all the scripts and styles needed to display the web page. When it has too much work to do, the thread is blocked and this delays the page load and will make it unresponsive.

This PageSpeed Insights Diagnostic will flag pages that keep the main thread busy for longer than 4 seconds during load and show a breakdown of where CPU time was spent while the browser loaded your page:

How to minimize main thread work with WP Rocket?

In this Diagnostic, PageSpeed Insights has sections based on the categories that Lighthouse reports. Let’s see which WP Rocket’s features can help in each section:

Script evaluation

• Minify CSS & Minify/Combine JS
• Delay JavaScript Execution

Style and layout & Rendering

• Automatic Lazy Rendering - Note: The improvements are especially noticeable when a page has several heavy HTML elements that had been lazily rendered.

WP Rocket can’t further help here, as it’s related to the DOM and to the layout structure. More details in these articles:

• Reduce the scope and complexity of style calculations
• Avoid large, complex layouts and layout thrashing

Parsing HTML and CSS

• Minify CSS
• Load CSS Asynchronously

Script parsing and compilation

• Minify/Combine JS 
• Load JavaScript deferred
• Delay JavaScript Execution

Garbage Collection

WP Rocket can’t help here as this is the time Chrome Browser spend to collect the memory usage : https://web.dev/monitor-total-page-memory-usage/

Additional Resources

• WP Rocket Core Web Vitals Hub - Minimize Main Thread Work
• https://web.dev/mainthread-work-breakdown/

Not a WP Rocket customer yet?
Read our article about How to minimize main thread work on WordPress and learn how to address this PageSpeed Insights recommendation with and without a plugin.