How Can You Minimize Render-Blocking JavaScript and CSS to Address Render Delay Warnings Provided by Google PageSpeed Insights?


Minimizing render-blocking JavaScript and CSS is crucial for optimizing webpage load times and improving performance scores on tools like Google PageSpeed Insights. This involves deferring non-critical resources, optimizing critical rendering paths, and careful management of web fonts. Here’s a comprehensive guide to help you address render delay warnings.

Deferring Non-Critical JavaScript

Use the defer Attribute

Add the defer attribute to your <script> tags to ensure scripts execute after the HTML is fully parsed.

<script src="example.js" defer></script>

This technique helps prioritize HTML rendering before executing JavaScript, [Defer Non-Critical JavaScript, 2023].

Load Non-Critical JavaScript Asynchronously

The async attribute allows scripts to download asynchronously without blocking HTML parsing.

<script src="example.js" async></script>

This can improve load times, especially for non-essential JavaScript code.

Optimizing CSS Delivery

Minify CSS

Minify your CSS files to reduce their size and remove unnecessary whitespace and comments, which helps in faster loading. Tools like CSSNano are commonly used for this purpose.

Inline Critical CSS

Extract and inline the critical CSS directly into the HTML <head> to ensure essential styles are loaded immediately.

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

Refer to the detailed guide on [Optimize CSS Delivery, 2022].

Defer Non-Critical CSS

Load non-critical CSS asynchronously using the loadCSS script or link elements with the media attribute set to "print" until fully loaded.

<link rel="stylesheet" href="non-critical.css" media="print" onload="'all'">

Optimizing Critical Rendering Path

Preload Key Resources

Use <link rel="preload"> to preload important resources, ensuring they fetch early in the page lifecycle.

<link rel="preload" href="styles.css" as="style"><link rel="preload" href="script.js" as="script">

Learn more from [Preload Critical Assets, 2022].

Inline Essential Styles and Scripts

Inline small essential styles and JavaScript directly within the HTML to reduce additional requests.

<style> /* Essential inline styles */ </style><script> // Inline essential scripts </script>

Refer to [Understanding the Critical Rendering Path, 2023] for an in-depth explanation.

Optimizing Web Fonts

Use font-display Swap

Make use of font-display: swap to prevent invisible text during the font loading process.

@font-face { font-family: 'Open Sans'; src: url('fonts/OpenSans.woff2') format('woff2'); font-display: swap; }

Detailed guidelines are available at [Web Font Optimization, 2023].

Subset Your Fonts

Load only required sets of characters or font subsets to reduce font size and loading times. Tools like GlyphHanger can help with creating subsets.

Preconnect to Font Sources

Use <link rel="preconnect"> to establish early connections to your font providers, reducing DNS lookup times and connection setup.

<link rel="preconnect" href="" crossorigin>

For more details, refer to [Preconnect and DNS Prefetch, 2022].


Minimizing render-blocking resources is essential to improve website performance and user experience. By deferring non-critical JavaScript, optimizing CSS delivery, managing the critical rendering path efficiently, and employing best practices for web fonts, you can significantly reduce render delays and enhance overall page speed.