SEO managers and web developers understand that responsive, fast-loading websites are crucial for both search engine rankings and user satisfaction. Page speed, in particular, plays a significant role in optimizing the SEO performance of JavaScript-heavy websites.
While various techniques can improve page speed, caching is particularly effective, especially for JS-based sites. When implemented properly, caching in JavaScript can boost your website rendering efficiency, enhance user experience, and ultimately improve search engine visibility.
In this JavaScript caching guide, we will explore caching’s effect on SEO, discuss the optimal ways to implement it, and highlight its importance in JavaScript.
What is Caching?
Caching is storing and reusing frequently accessed data of a website. To give more clarity, let’s use an analogy.
Imagine you have two boxes full of toys: one big and one small. Now, when you want to locate your favorite toys, it is faster and more resource-efficient to find them in a smaller than larger box.
Caching operates like a smaller box, acting as a personalized space where the webpage elements of your visited sites are stored for quicker access. This includes the images, scripts, stylesheets, and other webpage resources (in HTML, CSS, JavaScript, and other format).
This means that when a user visits a page, caching enables the browser to download and process these pre-saved files faster, instead of fetching and generating the same content from scratch repeatedly. Consequently, you’ll have quicker website rendering and higher PageSpeed. And since PageSpeed is a ranking factor, the faster your pages load, the better your SEO performance.
Pro tip: Get a deeper understanding of caching and how it impacts SEO in this in-depth article.
Impact of JavaScript Caches on SEO
As explained, one of the advantages of caching in JavaScript is that it prevents your site from spending unnecessary resources to reload the page and even speeds up the page loading time. From an SEO perspective, fast-loading pages lead to lower bounce rates and higher engagement—two factors that search engines consider when ranking websites.
Beyond speed improvements, caching in JavaScript also contributes to a more resilient web experience. For example, service workers (JavaScript files that run in the background of a web browser) can cache essential assets and dynamic data, enabling offline access and improving performance on slow networks. This simple feature ensures users can still interact with a JS site even when connectivity is unstable, which is especially valuable for mobile users.
The Problems with JavaScript Caching
Now, caching may be an excellent method to cut page load time, but it can be problematic when it comes to caching JavaScript files.
Effects of JavaScript Caching on Search Engine Crawling Process
While caching in JavaScript and Single-Page Applications (SPAs) speeds up page loads and creates a smoother user experience, it can cause unexpected hiccups when search engines crawl your site.
Search engine bots (like Googlebot) do generally respect cache headers, but if your JavaScript files or dynamic content are cached for too long, bots might keep seeing outdated data. This delay in updating can lead to stale information showing up in SERPs, which isn’t ideal if you’re trying to rank for fresh content or frequently changing pages.
Another issue is how search engine bots handle cached content. Even though modern search engine crawlers can execute JavaScript, they may not always re-fetch new scripts if the old ones are still valid according to your cache settings. As a result, important changes—like updated metadata, prices, or user-generated content—may go unnoticed for a while.
Effects of JavaScript Caching on User Experience
From the user’s perspective, caching JavaScript files can cause two main problems: cache invalidation and first-page load delay.
- Cache invalidation: when you update your JS-based website, users may not see the latest version. This is because the browser typically retrieves the cached version to lower the loading time.
- First-page load delay: every time a user visits a new website or just recently cleaned up their cache, the browser needs to fetch all the JS files again. Consequently, the heavier you rely on JS elements, the slower your page will load.
That said, there are some strategies to overcome JavaScript caching issues. This and methods to implement caching will be explained below.
How to Implement Caching?
There are three popular methods you can use to cache JavaScript files: LocalStorage, cache API, and prerendering service.
1. Caching Using LocalStorage
LocalStorage is a built-in web JS storage mechanism that allows you to store key-value pairs on the client side. It’s a simple way to cache small data, such as user preferences or tokens.
To implement caching through LocalStorage, web developers can check if the requested information is available on the platform. If it is, they can retrieve it directly from LocalStorage instead of making a network request. However, if the data is unavailable, they can fetch it from the central storage location and store it in LocalStorage for future use.
Here’s an example of caching using LocalStorage.
// Check if data is available in LocalStorage
const cachedData = localStorage.getItem('cachedData');
if (cachedData) {
// Data is available in LocalStorage, use it
const parsedData = JSON.parse(cachedData);
// Do something with the parsedData
console.log('Data retrieved from cache:', parsedData);
} else {
// Data is not available in LocalStorage, fetch it from the server
fetch('https://api.example.com/data')
.then(response => response.json())
.then(data => {
// Store the fetched data in LocalStorage for future use
localStorage.setItem('cachedData', JSON.stringify(data));
// Do something with the data
console.log('Data fetched from server:', data);
})
.catch(error => {
// Handle any errors
console.error('Error fetching data:', error);
});
}2. Using Cache API
Another popular method for caching JavaScript files is the Cache API. Cache API is a more advanced and powerful way to cache data and assets on the client side.
The Cache API is typically used to cache resources. It is particularly useful for Progressive Web Apps (PWAs) and websites that need to provide a dependable and fast user experience, even in offline or slow network conditions. This article will give you more information about working with cache API.
3. Using Prerender.io
The last method for caching is using a prerendering service like Prerender. Adopting Prerender is particularly useful for a heavy JS-based website since it solves JavaScript caching issues.
When a search engine bot initiates a page request, Prerender automatically crawls and caches the page. During this process, all the essential files for website rendering are downloaded and ready to be served to the bots when requested.
Consequently, Prerender helps solve JS caching problems and more:
- Schedule recaching
After you update your JS page, you can queue them to be recached. This will generate the latest cache data, guaranteeing that users will always see the latest content.
- Reduced first-page load time
Since Prerender takes and saves a snapshot of your pages in the HTML version, whenever bots request a page, they’ll be given the prerendered version. This drastically cut the website rendering time, resulting in faster page load time and response.
This blog will tell you more about how Prerender works and its effects on your website’s visibility and SEO performance.
Roles of Caching for Your Web Performance
There are many reasons caching can improve your web application performance, but here are the most important:
- Reduce server load
This is especially beneficial for high-traffic websites and applications, such as e-commerce websites. And since your server doesn’t do the heavy lifting, you can cut costs in upgrading and maintaining it.
- Improve SEO performance
JavaScript caching can dramatically improve your website’s SEO by making it load faster and feel smoother for visitors—two things search engines pay close attention to. It also helps your site perform better on Google’s Core Web Vitals, which measure how quickly your main content appears (Largest Contentful Paint), how soon the page is interactive (First Input Delay), and how stable the layout is (Cumulative Layout Shift).
By serving key resources like images, scripts, and styles from the cache (either locally or via edge servers), your site can load essential elements more quickly, respond faster to user interactions, and avoid sudden shifts in layout. When all these metrics look good, search engines see your site as more user-friendly, often boosting your rankings and overall visibility.
- Create robustness against heavy traffic
Caching allows a website to handle a larger number of users and traffic without the need to upgrade the server. This cost-effective scalability is essential for businesses with fluctuations in traffic (e.g., sudden traffic spikes) and websites with lots of dynamic content.
- Serve as failover
By implementing caching, you will create a redundancy and failover mechanism. This means that when the primary server or data source encounters some issues, such as downtime, the cached content can continue serving the visitors. This will prevent service interruptions and maintain a good user experience.
- Impact of Caching on Mobile SEO
On mobile devices, connections can be slow, and data might be limited, making caching especially valuable for mobile SEO. By storing key files (such as images and scripts) either on the user’s device or on nearby servers, your JS site loads faster, resulting in a smoother experience that lowers bounce rates, boosts engagement, and ultimately leads to better rankings in mobile search results.
3 Best Practices for Caching JavaScript Files
1. Limit Cache for Dynamic Data
Not all JavaScript files or responses should be cached forever, especially those fetching live data. Setting a shorter max-age or using no-cache headers for dynamic endpoints helps ensure fresh content. Tools like Chrome DevTools or Postman can help you confirm that dynamic data isn’t being over-cached.
2. Use Service Workers Wisely
Service workers can pre-cache critical files and support offline functionality, but improper configuration might lead to serving stale files. Implement a cache-first strategy for static assets while setting up clear rules to update service worker caches. In your browser’s developer tools, open the Application panel (in Chrome) to see which files the service worker is caching and verify they are updating correctly.
3. Version Your JavaScript Files
Including a version or hash in your filenames (e.g., app-v2.js or app.[hash].js) helps ensure that when you update your code, browsers fetch the new file instead of an old cached version. Build tools like Webpack or Parcel can automatically append unique hashes. To confirm it’s working, check the Network tab in your browser’s developer tools—if you see a new filename when you deploy, cache busting is in action.
Avoid Caching Irrelevant Pages (for SEO)
While caching website pages may be great for your enterprise SEO health, not all pages should be cached. This includes pages that collect sensitive or private information (e.g., login, user account, and checkout pages) and any single-use pages (e.g., pages to promote one-time events). Additionally, administrative or backend pages intended for website management should also be excluded from caching.
Selecting pages you want to include and exclude from the caching queue can be tedious. However, If you use Prerender, you can easily choose them from your dashboard.
Furthermore, Prerender is also handy for caching dynamic content pages. Its content freshness and recaching feature ensure that visitors will get the up-to-date content, not the outdated one.
Optimize JavaScript Caching for Better SEO Results
Caching is a valuable technique that can increase PageSpeed and SEO performance. Knowing what caching is, its roles, and the challenges in caching JavaScript files allows you to make informed decisions to best address your website caching needs and improve your SEO health.
Don’t let JavaScript caching issues block your web from showing up on the top SERPs. Adopt Prerender today and see the difference it can make. Start free with 1,000 free caches, and upgrade as you scale!
FAQs on JavaScript Caching and Its SEO Impact
Answering some questions about caching in JavaScript, its role in improving SEO performance, and Prerender.io.
1. Does Caching Impact SEO?
Since caching saves the rendered version of your website and serves it again when the same page is requested, it improves your site’s PageSpeed. And since PageSpeed is one of the most important SEO and ranking factors for Google SERPs, caching can significantly improve your SEO health.
2. Besides Improving SEO and Pagespeed, What Are Other Benefits of Caching?
Besides boosting your SEO and PageSpeed performance, caching can serve as a failover mechanism when your primary website server is down. This way, users can still be served the cached version of your content, maintaining a good user experience.
3. Does prerender.io Cache Websites?
Yes, Prerender.io caches websites as part of its pre-rendering process. The JavaScript content that Prerender.io rendered and turned into its HTML version is saved as cached and served to search engine crawlers whenever they request it. This eliminates the need for your sites to process requests from scratch, accelerating your server response time (SRT) to under 50 milliseconds. Learn more about how Prerender.io works here.
