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What is Preloading, and How Does it Impact Core Web Vitals and Your User Experience?
According to Google Search Console (GCS), one area of improvement I have on Martech Zone is improving my mobile performance as per Core Web Vitals (CWV), a set of metrics that Google uses to evaluate page performance and user experience. My site utilizes custom fonts, and I noticed that there’s quite a delay in loading the page on mobile devices because those fonts are loaded late via CSS. I was able to dramatically improve my mobile performance by preloading my fonts.
Table of Contents
- What is Preloading?
- How Does Preloading Impact Core Web Vitals?
- Understanding Render-Blocking
- When Should You Use Preloading?
- Advantages and Disadvantages of Preloading
- Advantages
- Disadvantages
- How to Write Preload Directives for Each Type of Asset
What is Preloading?
Preloading is a powerful technique used in web development to improve a website’s loading performance by instructing the browser to prioritize specific resources. By telling the browser to load certain assets earlier than it typically would, preloading enhances the user experience and can significantly impact
How Does Preloading Impact Core Web Vitals?
Core Web Vitals consist of three main metrics:
Understanding Render-Blocking
Certain resources, like CSS and JavaScript, can be render-blocking. The browser must load and process these files before displaying anything on the screen. For example, if a page’s main CSS file is render-blocking, the browser will wait to display it until it has fully downloaded and processed that CSS file. This waiting period can delay the page’s First Paint, or the moment when content first appears on the screen. By preloading render-blocking resources, you can reduce this waiting period and make your page appear faster.
When Should You Use Preloading?
Preloading is most effective when specific assets are essential to the initial rendering of your page. It’s beneficial to use preloading when:
Advantages and Disadvantages of Preloading
While preloading is an incredible tool, it can also be abused and cause other issues:
Advantages
Disadvantages
How to Write Preload Directives for Each Type of Asset
Different assets have unique requirements when it comes to preloading. Here’s a guide for setting up preloading for various types of resources:
1. Fonts
Custom fonts are often render-blocking, especially if essential for above-the-fold content. Users may experience a Flash of Unstyled Text (FOUT) when fonts load slowly, where fallback fonts display until the custom font loads. You can prevent this by using the tag with appropriate attributes:
By preloading fonts, you ensure they are available as soon as needed, preventing layout shifts and improving user experience. In WordPress, I was able to preload the fonts hosted on my server by including the following function in functions.php in my child theme.
Preload fonts from the site
function mtz_preload_fonts() {
$child_theme_uri = get_stylesheet_directory_uri();
// Preload each font on a separate line
echo '';
echo '';
echo '';
}
add_action('wp_head', 'mtz_preload_fonts');
2. Images
Preloading is ideal for critical images, such as a hero image at the top of the page. To preload images, use the tag with as="image":
However, limit preloading to only essential images. Loading too many images at once can overload the browser, delaying the page load.
3. CSS Stylesheets
CSS files are often render-blocking by default, meaning the browser must download and apply them before displaying any content. To help prioritize the main stylesheet, you can preload it with:
If you preload CSS, remember to include a regular tag for fallback purposes since the browser may not immediately apply preloaded stylesheets.
4. JavaScript Files
Preloading JavaScript is useful for scripts that must be executed immediately to ensure proper page functionality. Be mindful that JavaScript files can also be render-blocking, so it’s a good idea only to preload essential scripts:
Avoid preloading JavaScript files that aren’t crucial for initial page functionality. If the browser is overloaded with render-blocking scripts, this can slow down rendering.
Conclusion
Preloading is a valuable technique for optimizing a website’s loading performance and enhancing Core Web Vitals, particularly the LCP metric. When used thoughtfully, preloading critical resources ensures that essential content loads quickly, leading to a better user experience and potential SEO benefits. However, overusing preloading can backfire, slowing the page and wasting resources.
Focus on preloading only the most important above-the-fold assets, such as fonts, hero images, and essential CSS or JavaScript files. By understanding which resources are render-blocking and implementing preloading strategically, you can make your website load faster, creating a smoother user experience and increasing your site’s visibility in search results.
©2024 DK New Media, LLC, All rights reserved | Disclosure
Originally Published on Martech Zone: What is Preloading, and How Does it Impact Core Web Vitals and Your User Experience?
View all episodes
By Douglas Karr
4.7
1111 ratings
According to Google Search Console (GCS), one area of improvement I have on Martech Zone is improving my mobile performance as per Core Web Vitals (CWV), a set of metrics that Google uses to evaluate page performance and user experience. My site utilizes custom fonts, and I noticed that there’s quite a delay in loading the page on mobile devices because those fonts are loaded late via CSS. I was able to dramatically improve my mobile performance by preloading my fonts.
Table of Contents
- What is Preloading?
- How Does Preloading Impact Core Web Vitals?
- Understanding Render-Blocking
- When Should You Use Preloading?
- Advantages and Disadvantages of Preloading
- Advantages
- Disadvantages
- How to Write Preload Directives for Each Type of Asset
What is Preloading?
Preloading is a powerful technique used in web development to improve a website’s loading performance by instructing the browser to prioritize specific resources. By telling the browser to load certain assets earlier than it typically would, preloading enhances the user experience and can significantly impact
How Does Preloading Impact Core Web Vitals?
Core Web Vitals consist of three main metrics:
Understanding Render-Blocking
Certain resources, like CSS and JavaScript, can be render-blocking. The browser must load and process these files before displaying anything on the screen. For example, if a page’s main CSS file is render-blocking, the browser will wait to display it until it has fully downloaded and processed that CSS file. This waiting period can delay the page’s First Paint, or the moment when content first appears on the screen. By preloading render-blocking resources, you can reduce this waiting period and make your page appear faster.
When Should You Use Preloading?
Preloading is most effective when specific assets are essential to the initial rendering of your page. It’s beneficial to use preloading when:
Advantages and Disadvantages of Preloading
While preloading is an incredible tool, it can also be abused and cause other issues:
Advantages
Disadvantages
How to Write Preload Directives for Each Type of Asset
Different assets have unique requirements when it comes to preloading. Here’s a guide for setting up preloading for various types of resources:
1. Fonts
Custom fonts are often render-blocking, especially if essential for above-the-fold content. Users may experience a Flash of Unstyled Text (FOUT) when fonts load slowly, where fallback fonts display until the custom font loads. You can prevent this by using the tag with appropriate attributes:
By preloading fonts, you ensure they are available as soon as needed, preventing layout shifts and improving user experience. In WordPress, I was able to preload the fonts hosted on my server by including the following function in functions.php in my child theme.
Preload fonts from the site
function mtz_preload_fonts() {
$child_theme_uri = get_stylesheet_directory_uri();
// Preload each font on a separate line
echo '';
echo '';
echo '';
}
add_action('wp_head', 'mtz_preload_fonts');
2. Images
Preloading is ideal for critical images, such as a hero image at the top of the page. To preload images, use the tag with as="image":
However, limit preloading to only essential images. Loading too many images at once can overload the browser, delaying the page load.
3. CSS Stylesheets
CSS files are often render-blocking by default, meaning the browser must download and apply them before displaying any content. To help prioritize the main stylesheet, you can preload it with:
If you preload CSS, remember to include a regular tag for fallback purposes since the browser may not immediately apply preloaded stylesheets.
4. JavaScript Files
Preloading JavaScript is useful for scripts that must be executed immediately to ensure proper page functionality. Be mindful that JavaScript files can also be render-blocking, so it’s a good idea only to preload essential scripts:
Avoid preloading JavaScript files that aren’t crucial for initial page functionality. If the browser is overloaded with render-blocking scripts, this can slow down rendering.
Conclusion
Preloading is a valuable technique for optimizing a website’s loading performance and enhancing Core Web Vitals, particularly the LCP metric. When used thoughtfully, preloading critical resources ensures that essential content loads quickly, leading to a better user experience and potential SEO benefits. However, overusing preloading can backfire, slowing the page and wasting resources.
Focus on preloading only the most important above-the-fold assets, such as fonts, hero images, and essential CSS or JavaScript files. By understanding which resources are render-blocking and implementing preloading strategically, you can make your website load faster, creating a smoother user experience and increasing your site’s visibility in search results.
©2024 DK New Media, LLC, All rights reserved | Disclosure
Originally Published on Martech Zone: What is Preloading, and How Does it Impact Core Web Vitals and Your User Experience?