CSS however can benefit from an extra step - identifying and separating high and low priority resources and loading them accordingly. The exact CSS and JavaScript considered high priority or critical will depend on the content, layout and functionality of each page, but will likely focus on above-the-fold content elements.Įliminating render blocking resources is important for both CSS and JavaScript, but most (if not all) JavaScript can be safely deferred to load in the background and run toward the end of the loading process. Lower-priority CSS and JavaScript resources that are not essential to the initially-visible part of the page can then be loaded in the background without render blocking and apply to the page later in the loading process. Rather than loading all files before the page is displayed on screen, a more efficient, user-friendly strategy is to structure the loading process to prioritize only the most critical resources to load as soon as possible. On most webpages, the majority of the total CSS and JavaScript loaded by the browser isn't needed to display only the initially-visible or above-the-fold parts of the page, so it makes sense to load these resources with appropriate priority.
However as content and features become more complex and CSS and JavaScript files become larger, more numerous or loaded over slower internet speeds, the effect of render blocking resources on page speed becomes significant.Įliminating render blocking resources is the foundation of a progressive approach to page loading. A Progressive Approachįor very simple pages with only a few small files transferred over a fast internet connection, the loading process is nearly instantaneous. Eliminating render blocking resources is essential to minimize this delay so the page can load and display content as soon as possible. The result is a delay in the display of content to the user, during which time the page may appear blank or incomplete. Render blocking refers to the way conventional CSS and JavaScript references interrupt the rendering process while those resources load and apply to the page.
This sequence of interpreting the page and its resources into the content displayed on screen is known as the critical rendering path and is important for page speed, particularly the initially-visible, above-the-fold content. Any external resources referenced in the HTML like CSS, JavaScript files and images are downloaded and applied to the page. When a user navigates to a page, the web browser first loads and examines the HTML code. To make the needed changes and get the best results, it can help to take a closer look at render blocking and why it matters. Avoiding or eliminating render blocking resources altogether is a powerful strategy to maximize website speed and ace speed tests. If you've run a website loading speed test like Google's PageSpeed Insights, you may have seen an opportunity noted in the test results like Eliminate render-blocking resources. Optimizing the structure of file references in the HTML is an important step to streamline the loading process and ensure that pages load quickly and efficiently.
Javascript run as soon as element renders code#
HTML code is the foundation of each page and coordinates how those resources are loaded. The file resources of a website like HTML, CSS and JavaScript work together to form the content, visual styling and functionality users see and interact with in the browser. Fix & Eliminate Render Blocking Resources Page Speed Checklistįix and eliminate render blocking resources by reconfiguring the loading process with a progressive approach - separating and loading critical and non-critical resources with appropriate priority.
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