Is your WordPress site taking too long to load? Render-blocking JavaScript and CSS could be the culprit. These files can slow down your page speed and negatively impact user experience. But don‘t worry – in this comprehensive guide, I‘ll show you how to eliminate render-blocking resources and achieve a better PageSpeed score.
Why Render-Blocking Resources Are a Problem
When a web page loads, the browser must parse the HTML and construct the Document Object Model (DOM) before it can render any content. If it encounters a script or stylesheet, it has to stop and execute that file first. These render-blocking resources delay the First Contentful Paint (FCP), which is when the browser displays the first bit of content on the screen.
Why is this an issue? A study by Google found that as page load time goes from 1 second to 3 seconds, the probability of a bounce increases 32%. At 5 seconds, the probability of bounce increases 90%. In other words, slow-loading pages frustrate users and cause them to leave your site.
Eliminating render-blocking resources is crucial for delivering a fast, seamless user experience. It‘s also a key metric search engines use to rank pages. Google has stated that page speed is a ranking factor for both desktop and mobile searches. So optimizing your WordPress site‘s JavaScript and CSS is important not just for user experience but also for SEO.
Identifying Render-Blocking JavaScript and CSS
So how do you know if your WordPress site has render-blocking resources? The easiest way is to run your URL through Google‘s PageSpeed Insights tool. It will analyze your page and flag any scripts or stylesheets that are blocking the initial render.
Here‘s an example of render-blocking resources identified by PageSpeed Insights:
As you can see, it lists the specific JS and CSS files that need to be optimized. It also provides recommendations like "Defer unused CSS" and "Minimize critical requests depth".
Another helpful tool is GTmetrix, which grades your site‘s performance and provides actionable recommendations. Under the "Structure" tab, it highlights render-blocking JavaScript and CSS:
For a more granular, developer-oriented approach, you can use your browser‘s Developer Tools. In Chrome, open DevTools and go to the "Network" tab. Reload your page and observe the waterfall chart. Render-blocking resources will be listed before the "DOMContentLoaded" event.
Now that you know which files are causing issues, let‘s look at how to fix them.
Fixing Render-Blocking Resources in WordPress
There are a few different ways to eliminate render-blocking JavaScript and CSS in WordPress, depending on your technical expertise and preferences.
Method 1: Use a Plugin
For beginners, the simplest approach is to use a WordPress performance plugin that can automatically optimize your site‘s JS and CSS files. Two of the most popular options are WP Rocket and Autoptimize.
WP Rocket
WP Rocket is a premium caching and optimization plugin that can minify, combine, and defer your JavaScript and CSS files with minimal configuration.
- Install and activate the WP Rocket plugin.
- Go to Settings > WP Rocket and click the "File Optimization" tab.
- Under "CSS Files", enable Minification, Combine CSS files, and Optimize CSS delivery.
- Under "JavaScript Files", enable Minification, Combine JavaScript files, Load JavaScript deferred, and Delay JavaScript execution.
- Click "Save Changes".
After enabling these options, WP Rocket will minify your JS and CSS, combine them into fewer files, and defer their loading so they don‘t block rendering.
Be sure to test your site thoroughly after enabling optimizations. In some cases, optimizing scripts or styles can break functionality. WP Rocket has a "Safe Mode" option to revert changes if needed, as well as an "Exclude" list where you can specify files to skip.
Autoptimize
Autoptimize is a free plugin that focuses solely on optimizing scripts and styles. It can aggregate, minify and cache your JS and CSS files.
- Install and activate the Autoptimize plugin.
- Go to Settings > Autoptimize.
- Check the boxes for "Optimize JavaScript Code" and "Optimize CSS Code".
- For best results, also enable "Aggregate JS-files" and "Aggregate CSS-files".
- Click "Save Changes and Empty Cache".
Like with WP Rocket, it‘s important to test your site after enabling these optimizations. Autoptimize has advanced configuration options to exclude specific scripts or styles if you encounter issues.
Method 2: Manual Optimization
For more advanced users comfortable editing code, you can manually optimize your WordPress theme and plugin files to eliminate render blocking issues. This gives you fine-grained control but requires a development skillset.
Here are a few key tactics:
Minification
Minification removes unnecessary characters like whitespace, comments and formatting from your code to reduce file size without changing functionality. Smaller files download faster.
For JavaScript, you can use tools like Closure Compiler or UglifyJS. For CSS, try clean-css or CSSO.
Here‘s an example of minified CSS:
.header{background:#000;color:#fff;padding:10px}.nav{margin:0;padding:0;list-style:none}.nav li{display:inline-block;margin-right:10px}Compare that to the original, unminified version:
.header {
background: #000;
color: #fff;
padding: 10px;
}
.nav {
margin: 0;
padding: 0;
list-style: none;
}
.nav li {
display: inline-block;
margin-right: 10px;
}As you can see, minification significantly reduces the amount of code without altering how it works.
File Combining
Having multiple JS or CSS files can slow down your site, as each one requires a separate HTTP request. Combining (or concatenating) them into a single file reduces the number of requests needed.
For example, let‘s say your WordPress site loads these stylesheets:
<link rel="stylesheet" href="style1.css">
<link rel="stylesheet" href="style2.css">
<link rel="stylesheet" href="style3.css">You could use a build tool like Gulp or Grunt to combine those into one CSS file:
const gulp = require(‘gulp‘);
const concat = require(‘gulp-concat‘);
gulp.task(‘css‘, function() {
return gulp.src(‘./css/*.css‘)
.pipe(concat(‘all-styles.css‘))
.pipe(gulp.dest(‘./dist/‘));
});Then reference the combined file in your HTML instead:
<link rel="stylesheet" href="all-styles.css">One HTTP request instead of three means faster loading.
Defer and Async
By default, JavaScript files are loaded synchronously. The browser must download, parse and execute them before it can continue rendering the page. This behavior is render-blocking.
There are two attributes you can add to your <script> tags to change this default behavior: defer and async.
Scripts loaded with the defer attribute will only execute after the document has finished parsing. This allows the browser to render the page first and then run the scripts afterwards. Deferred scripts still execute in order.
<script defer src="myscript.js">Scripts loaded with the async attribute will download without blocking rendering and then execute as soon as they finish downloading. Async scripts can execute out of order.
<script async src="myscript.js">Both of these attributes can help eliminate render-blocking JavaScript issues. The choice between defer and async depends on whether your scripts need to execute in a specific order and if they are critical for page functionality.
In general, any scripts that don‘t impact content above-the-fold are good candidates for deferred or async loading. Common examples are analytics scripts, ads, and social media buttons.
One caveat is that these attributes only work on externally linked scripts, not inline JavaScript. Also, be aware that defer and async are ignored for scripts that don‘t have a src attribute.
Inline Critical CSS
Some of your CSS is considered "critical" if it styles content that appears above-the-fold (the portion of the page visible without scrolling). This critical CSS should be loaded as quickly as possible to avoid a flash of unstyled content (FOUC).
You can inline your critical CSS directly in the <head> of your HTML instead of referencing an external stylesheet. This eliminates a render-blocking file request.
Here‘s an example of inlined critical CSS:
<style>
/* Critical CSS here */
.hero {
background: url(‘hero.jpg‘) center/cover;
height: 100vh;
}
.hero h1 {
color: #fff;
font-size: 4rem;
margin-top: 2rem;
}
</style>To identify which styles are critical, you can use a tool like critical. It extracts the styles needed to render above-the-fold content based on your specific page.
Then load the rest of your non-critical CSS asynchronously using a tool like loadCSS. Here‘s an example:
<link rel="preload" href="non-critical.css" as="style" onload="this.onload=null;this.rel=‘stylesheet‘">
<noscript><link rel="stylesheet" href="non-critical.css"></noscript>This approach ensures your critical CSS loads instantly while the non-critical CSS is deferred to avoid blocking the initial render.
Other Tips and Considerations
- If you‘re using a lot of third-party scripts or stylesheets (Google Fonts, analytics, ads, etc.), consider using a service like CDNJS to load them from a fast, reliable content delivery network (CDN).
- Regularly audit your WordPress plugins and remove any that are unnecessary or not actively maintained. Too many plugins, especially poorly coded ones, can slow down your site.
- Lazy load images and videos so they don‘t load until a user scrolls to them. This can significantly speed up initial page load. WordPress plugins like WP Smush or a3 Lazy Load can handle this for you.
- Use a tool like Lighthouse to regularly audit your WordPress site for performance issues. It provides detailed recommendations and insights.
- Remember that a perfect PageSpeed score of 100 is not always achievable or necessary. The goal is to optimize the user experience as much as possible while still delivering the features and design your site needs. Obsessing over a few extra points can lead to diminishing returns.
Test, Monitor, Iterate
Eliminating render-blocking JavaScript and CSS is an ongoing process, not a one-time fix. As you update your WordPress theme and plugins or add new features to your site, be sure to re-test your speed regularly.
Tools like PageSpeed Insights and GTmetrix make it easy to benchmark your optimizations and catch any regressions. You can also use services like Pingdom to monitor your page speed over time.
Remember to test your site on a variety of devices and connection speeds. A site that loads quickly on your fast office wifi may be frustratingly slow for a mobile user on 3G. Google‘s Test My Site tool can show you how your site performs on different mobile networks.
Finally, don‘t forget to get feedback from your actual users. Tools can provide valuable data, but nothing beats real-world testing. Consider adding a feedback form or survey to gather insights on how people experience your site‘s speed and usability.
Conclusion
By now, you should have a solid understanding of what render-blocking JavaScript and CSS are, how to identify them on your WordPress site, and multiple ways to eliminate them.
Remember, the goal of eliminating render-blocking resources is to provide a faster, smoother experience for your users. Faster pages lead to higher engagement, better conversions, and improved search engine rankings.
Whether you choose to use a plugin or optimize your code manually, the tactics outlined in this guide can help you measurably improve your WordPress site‘s performance. The key is to test thoroughly, monitor your progress over time, and always put the user experience first.
It takes some effort to eliminate render-blocking scripts and stylesheets, but the payoff — a faster site and happier users — is well worth it. So what are you waiting for? Go optimize your WordPress site‘s speed today!
