Render-blocking resources are elements like JavaScript and CSS that can prevent a webpage from displaying content to the user until they are fully loaded. Eliminating or minimizing these resources can significantly speed up the time it takes for a page to become interactive. Here's how you can tackle render-blocking resources:
1. Minimize Critical CSS and JavaScript
Identify Critical CSS: Only include the CSS needed to render the above-the-fold content inline within the
<head>tag. Tools like Critical can help you identify and extract this CSS.Defer Non-Critical CSS: Load non-critical CSS asynchronously using the
mediaattribute or loading them with JavaScript.
2. Use the async and defer Attributes for JavaScript
async: This attribute allows the script to be downloaded in the background without blocking the page render. Once downloaded, it will halt rendering to execute, then continue.<script async src="script.js"></script>defer: The script will be downloaded in the background likeasync, but execution is deferred until the HTML parsing is completed.<script defer src="script.js"></script>
3. Load Non-Critical JavaScript After Page Load
Utilize Event Handlers: You can create event listeners to load non-essential scripts after the
window.onloadevent or when the user interacts with a specific part of the page.
4. Implement Lazy Loading for Non-Essential Resources
Images and Media: Consider lazy loading images, videos, and other media that are not immediately visible to the user.
5. Minimize the Number of Requests
Combine Files: Where possible, combine smaller CSS and JavaScript files into single, larger files to reduce the number of HTTP requests.
Use Sprites for Images: Combining smaller images into sprites can also reduce the number of requests.
6. Utilize Server Push (HTTP/2)
Preload Important Resources: With HTTP/2 Server Push, you can preload essential resources, ensuring they're ready when needed.
7. Avoid or Minimize the Use of Blocking Third-Party Scripts
Evaluate Third-Party Scripts: Analyze third-party scripts like analytics, ads, or widgets, and load them asynchronously when possible.
8. Optimize Web Fonts
Use
font-display: swap;: This CSS feature allows a fallback font to be displayed until the custom font is loaded.Preload Key Web Fonts: If a specific font is crucial for your design, consider preloading it using
<link rel="preload">.
Conclusion
Eliminating render-blocking resources requires a strategic approach, considering the balance between aesthetics, functionality, and performance. Implementing these techniques can dramatically improve the perceived performance of your site, leading to a more engaging user experience.
