Step-by-step Guide to Lazy Loading Above Fold Css Resources

by

Lazy loading above the fold CSS resources is an effective technique to improve your website’s load time and user experience. By deferring the loading of CSS that is not immediately needed, you can reduce render-blocking and speed up the initial display of your webpage. This guide provides a step-by-step approach to implement lazy loading for above the fold CSS.

Understanding Above the Fold CSS

Above the fold CSS refers to the styles required to render the content visible in the initial viewport of the webpage. Loading this CSS promptly ensures that users see meaningful content quickly. Non-essential CSS can be deferred to improve performance, especially on mobile devices or slow networks.

Step 1: Identify Critical and Non-Critical CSS

The first step is to analyze your webpage and distinguish between critical above the fold CSS and non-critical CSS. Tools like Google PageSpeed Insights or Web.dev Critical CSS Generator can help automate this process. Extract the critical CSS and inline it into your HTML to ensure immediate rendering.

Step 2: Inline Critical CSS

Embed the critical CSS directly in the <head> section of your HTML document. This guarantees that essential styles are loaded immediately, reducing render-blocking. For example:

<style> /* Critical CSS here */ </style>

Step 3: Lazy Load Non-Critical CSS

For the non-critical CSS, instead of loading it synchronously, load it asynchronously using JavaScript. One common method is to create a <link> element with a rel attribute set to preload and then switch it to stylesheet once loaded:

<link rel=”preload” href=”styles.css” as=”style” onload=”this.rel=’stylesheet'”>

Ensure you include a noscript fallback for users with JavaScript disabled:

<noscript>

<link rel=”stylesheet” href=”styles.css”>

Step 4: Implement Lazy Loading in WordPress

In WordPress, you can enqueue your CSS files with custom attributes using wp_enqueue_style and add JavaScript to handle the lazy loading. For example, enqueue your CSS without loading it immediately and then load it asynchronously with JavaScript.

Sample code snippet:

functions.php

add_action(‘wp_enqueue_scripts’, function() {

  wp_register_style(‘lazy-style’, get_template_directory_uri() . ‘/styles.css’, [], null, ‘all’);

  wp_enqueue_style(‘lazy-style’);

});

Then, add JavaScript to load the stylesheet asynchronously.

In footer or a custom JS file:

var loadCSS = function() {

  var head = document.getElementsByTagName(‘head’)[0];

  var link = document.createElement(‘link’);

  link.rel = ‘stylesheet’;

  link.href = ‘YOUR_STYLESHEET_URL’;

  head.appendChild(link);

};

window.addEventListener(‘load’, loadCSS);

Step 5: Test and Optimize

After implementing lazy loading, test your website using tools like Google PageSpeed Insights, Lighthouse, or WebPageTest. Ensure that critical content loads quickly and non-critical CSS loads asynchronously without causing visual issues.

Continuously monitor performance and make adjustments as needed. Lazy loading CSS can significantly enhance your site’s speed when done correctly.