How to Reduce Page Load Time in JavaScript (6 Easy Fixes)
Melwyn Joseph
03 April 2025 | 7 minute read
JavaScript is essential for adding interactivity and functionality to websites, but if it’s not optimised, it can slow down your site. This slowdown can lead to a poor user experience, higher bounce rates, lower conversions and engagement, and even hurt your SEO rankings.
The good news is, improving JavaScript performance is easier than you might think. In this guide, we’ll share six easy and effective ways to reduce JavaScript load time – along with the tools you can use – to help you make your website faster and smoother.
How to Reduce Page Load Time in JavaScript
To reduce page load time in JavaScript, you need to optimise how your scripts are written, loaded, and delivered so that they don’t block or delay your page content. Below, we’ve listed six practical tips you can follow to reduce JavaScript load time.
6 Tips to Reduce Page Load Time in JavaScript
- Minify and compress your JavaScript files to reduce file size and speed up downloads.
- Defer or async your JavaScript loading to prevent blocking page rendering.
- Lazy load JavaScript when needed to avoid loading unnecessary scripts upfront.
- Remove unused JavaScript and dependencies to eliminate unnecessary code execution.
- Split JavaScript code and preload critical scripts to prioritise essential functionality.
- Use a content delivery network (CDN) to deliver JavaScript faster.
Now, let’s dive deeper into each of these tips.
Tip 1: Minify and Compress All JavaScript Files
Big, messy JavaScript files slow everything down. When your JS files are bloated with spaces, comments, and extra code, your users end up waiting longer for your site to load. The browser has to download, parse, and execute all that extra weight.
By cleaning things up, you’re giving your visitors a faster, smoother experience.
How to do it:
- Use a tool like UglifyJS to minify your JavaScript. This removes unnecessary spaces and comments.
- If you’re using WordPress, plugins like WP Rocket can automatically minify your JavaScript files with a single click.
- Turn on Gzip or Brotli compression on your server to make those files even smaller.
- Do a quick cleanup and remove old code, commented-out blocks, and unused variables.
Tip 2: Defer or Async JavaScript Loading
Here’s something many websites get wrong – they load all their JavaScript upfront, and the browser has to stop rendering the page to process it. That’s why sometimes you stare at a blank screen waiting for something to happen.
By deferring or async-loading your scripts, you let the browser load the content first and deal with the JavaScript later.
How to do it:
- Add the
deferattribute to important scripts so they load after the HTML is parsed. For example:<script src="main.js" defer></script> - For third-party scripts like analytics or chat widgets, use
asyncso they load independently. For example:<script src="analytics.js" async></script> - If you’re on WordPress, WP Rocket has an option to load JavaScript deferred automatically.
- Run a Lighthouse audit to identify scripts that block page rendering.
Tip 3: Lazy Load JavaScript When Needed
Think about it – why load everything upfront if the user might never use half of it? Things like sliders, modals, or chat widgets don’t need to load immediately.
If you lazy load these scripts, your site feels much faster because the browser isn’t bogged down loading stuff the user hasn’t asked for yet.
How to do it:
- Delay loading interactive elements like sliders, modals, or chat widgets until the user scrolls or clicks.
- In WordPress, enable LazyLoad in WP Rocket – it can automatically handle lazy loading for images, iframes, and JavaScript.
- Use a library like LoadJS if you’re building without WordPress.
Tip 4: Remove Unused JavaScript and Reduce Dependencies
Over time, your website can become a bit of a JavaScript graveyard – old plugins, unused libraries, and leftover code hanging around doing nothing but slowing things down. Every extra line of JS means more to download, parse, and execute. Cleaning it up makes your site leaner and faster.
How to do it:
- Open up Chrome DevTools → Coverage Tab and check how much of your JavaScript is actually being used.
- Get rid of plugins and libraries you’re not using anymore.
- Use Bundlephobia to see how much weight each npm package adds to your bundle.
- Wherever possible, ditch unnecessary JavaScript and use HTML/CSS instead.
Tip 5: Split Your JavaScript and Preload What’s Critical
If your entire site runs off one giant JavaScript file, visitors will have to wait until everything is downloaded and executed, even if they only need a tiny part of it to get started.
By splitting your JavaScript and preloading what’s really important, you can speed up how fast your page becomes interactive.
How to do it:
- Use code splitting in your build tool (like Webpack or Vite) to break up your JavaScript into smaller chunks.
- Preload your most important scripts using:
<link rel="preload" href="/main.js" as="script"> - Move non-essential JavaScript to the end of the page or load it after the main content.
Tip 6: Use a Content Delivery Network (CDN) for Faster Delivery
No matter how optimised your JavaScript is, users who are physically far from your server will experience slower load times. That’s where a CDN comes in. A CDN stores copies of your files on servers worldwide so users get faster access, wherever they are.
How to do it:
- Set up a CDN like Cloudflare, BunnyCDN, or KeyCDN to deliver your JavaScript and other static files.
- Many performance plugins like WP Rocket also offer seamless CDN integration, so you can connect your CDN without complex configuration.
- Make sure JavaScript, CSS, and image files are served from the CDN to minimise server response time.
Why Reducing JavaScript Load Time Matters
JavaScript load time directly affects your website’s overall load time and response time. When JavaScript takes too long to load or execute, it slows down how quickly your page appears and responds.
This impacts the user experience – and when users face delays, they’re more likely to leave your website, stop engaging, or not complete actions like signing up or making a purchase. That’s why reducing JavaScript load time matters.
Here’s why it matters specifically:
- Better user experience: Faster-loading pages keep visitors engaged and happy.
- Improved SEO: Google considers page speed and Core Web Vitals as ranking factors.
- Lower bounce rates: Slow websites drive users away before they even see your content.
- Higher conversion rates: A faster site means users are more likely to stay, browse, and take action.
When your JavaScript loads quickly, your content appears sooner, users can interact without delay, and your site feels smoother overall. In a world where every millisecond matters, optimising your JavaScript can be the difference between a visitor who stays and one who leaves.
How WebYes Can Help You Reduce JavaScript Load Time
Optimising JavaScript can be time-consuming, especially if you’re not sure where the issues are. That’s where WebYes can make the process easier. Our website audits automatically scan for common JavaScript-related issues that may be slowing down your site.
Specifically, WebYes checks for:
- Unminified JavaScript: Scripts that haven’t been compressed and are increasing file size unnecessarily.
- Unused JavaScript: Code that’s loaded but never used, wasting bandwidth and slowing down the page.
- Duplicated JavaScript: Multiple instances of the same script that bloat your pages.
- Legacy JavaScript: Outdated scripts that may slow down modern browsers and affect performance.
Want to see if your website has any of these JavaScript issues? Use the scanner below to instantly detect unminified, unused, duplicated, or outdated JavaScript on your site. Just enter your URL and get quick, actionable suggestions.
Article by
Melwyn holds a Bachelor's degree in Computer Science and has been writing professionally for over 4 years. He has a strong background in SEO and is certified in web accessibility from the World Wide Web Consortium (W3C). When he's not writing about website optimisation, you can find him enjoying a game of FIFA or exploring the open world of GTA.
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