Render-Blocking Resources

Render-blocking resources are elements that delay a webpage's loading efficiently. Typically consisting of JavaScript and CSS files, the browser must fully download, pars, and execute these resources before the page content can be displayed. Until the elements are completely processed, the browser's initial rendering is blocked, resulting in slower load times.

Purpose of Render Blocking Resources

The browser needs specific resources to process the critical rendering path of a webpage. Such resources are essential for the webpage to be displayed correctly and to function as intended. However, due to their loading behavior, the resources must be managed and optimized correctly. Otherwise, they can negatively impact website performance and increase load times.

Types of Rendering Blockers

CSS files, JavaScript files, and web fonts are typically rendering blockers.

CSS Files

CSS files define a webpage's visual layout and styling, including layouts, colors, and animations. CSS can be included in a webpage in three different ways:

  1. External stylesheets: loaded via <link> tags in the <head> section.
  2. Internal CSS: written within <style> tags, typically in the <head> section of the HTML.
  3. CSS imports: included using @import statements within a CSS file or <style> tags.

JavaScript Files

JavaScript files allow dynamic and interactive functionality on webpages, like real-time updates or animations, providing an inviting and functional user experience. There are different ways to include JavaScript in a webpage:

  1. External JavaScript: linked via \