JavaScript has enabled highly interactive and dynamic websites. But it also presents a challenge: ensuring your site is crawlable, indexable, and fast.
That’s why JavaScript SEO is essential.
When applied correctly, these strategies can significantly boost organic search performance.
For instance, book retailer Follet saw a remarkable recovery after fixing JavaScript issues:
That’s the impact of effective JavaScript SEO.
In this guide, you’ll:
- Get an introduction to JavaScript SEO
- Understand the challenges with using JavaScript for search
- Learn best practices to optimize your JavaScript site for organic search
What Is JavaScript SEO?
JavaScript SEO is the process of optimizing JavaScript websites. It ensures search engines can crawl, render, and index them.
Aligning JavaScript websites with SEO best practices can boost organic search rankings. All without hurting the user experience.
However, there are still uncertainties surrounding JavaScript and SEO’s impact.
Common JavaScript Misconceptions
| Misconception | Reality |
|---|---|
| Google can handle all JavaScript perfectly. | Since JavaScript is rendered in two phases, delays and errors can occur. These issues can stop Google from crawling, rendering, and indexing content, hurting rankings. |
| JavaScript is only for large sites. | JavaScript is versatile and benefits websites of varying sizes. Smaller sites can use JavaScript in interactive forms, content accordions, and navigation dropdowns |
| JavaScript SEO is optional. | JavaScript SEO is key for finding and indexing content, especially on JavaScript-heavy sites. |
Benefits of JavaScript SEO
Optimizing JavaScript for SEO can offer several advantages:
- Improved visibility: Crawled and indexed JavaScript content can boost search rankings
- Enhanced performance: Techniques like code splitting deliver only the important JavaScript code. This speeds up the site and reduces load times.
- Stronger collaboration: JavaScript SEO encourages SEOs, developers, and web teams to work together. This helps improve communication and alignment on your SEO project plan.
- Enhanced user experience: JavaScript boosts UX with smooth transitions and interactivity. It also speeds up and makes navigation between webpages more dynamic.
How Search Engines Render JavaScript
To understand JavaScript’s SEO impact, let’s explore how search engines process JavaScript pages.
Google has outlined that it processes JavaScript websites in three phases:
- Crawling
- Processing
- Indexing
Crawling
When Google finds a URL, it checks the robots.txt file and meta robots tags. This is to see if any content is blocked from being crawled or rendered.
If a link is discoverable by Google, the URL is added to a queue for simultaneous crawling and rendering.
Rendering
For traditional HTML websites, content is immediately available from the server response.
In JavaScript websites, Google must execute JavaScript to render and index the content. Due to resource demands, rendering is deferred until resources are available with Chromium.
Indexing
Once rendered, Googlebot reads the HTML, adds new links to the crawl list, and indexes the content.
How JavaScript Affects SEO
Despite its growing popularity, the question often arises: Is JavaScript bad for SEO?
Let’s examine aspects that can severely impact SEO if you don’t optimize JavaScript for search.
Rendering Delays
For Single Page Applications (SPAs) — like Gmail or Twitter, where content updates without page refreshes — JavaScript controls the content and user experience.
If Googlebot can’t execute the JavaScript, it may show a blank page.
This happens when Google struggles to process the JavaScript. It hurts the page’s visibility and organic performance.
To test how Google will see your SPA site if it can’t execute JavaScript, use the web crawler Screaming Frog. Configure the render settings to “Text Only” and crawl your site.
Indexing Issues
JavaScript frameworks (like React or Angular, which help build interactive websites) can make it harder for Google to read and index content.
For example, Follet’s online bookstore migrated millions of pages to a JavaScript framework.
Google had trouble processing the JavaScript, causing a sharp decline in organic performance:
Crawl Budget Challenges
Websites have a crawl budget. This refers to the number of pages Googlebot can crawl and index within a given timeframe.
Large JavaScript files consume significant crawling resources. They also limit Google’s ability to explore deeper pages on the site.
Core Web Vitals Concerns
JavaScript can affect how quickly the main content of a web page is loaded. This affects Largest Contentful Paint (LCP), a Core Web Vitals score.
For example, check out this performance timeline:
Section #4 (“Element Render Delay”) shows a JavaScript-induced delay in rendering an element.
This negatively impacts the LCP score.
JavaScript Rendering Options
When rendering webpages, you can choose from three options:
Server-Side Rendering (SSR), Client-Side Rendering (CSR), or Dynamic Rendering.
Let’s break down the key differences between them.
Server-Side Rendering (SSR)
SSR creates the full HTML on the server. It then sends this HTML directly to the client, like a browser or Googlebot.
This approach means the client doesn’t need to render the content.
As a result, the website loads faster and offers a smoother experience.
| Benefits of SSR | Drawbacks of SSR |
|---|---|
| Improved performance | Higher server load |
| Search engine optimization | Longer time to interactivity |
| Enhanced accessibility | Complex implementation |
| Consistent experience | Limited caching |
Client-Side Rendering (CSR)
In CSR, the client—like a user, browser, or Googlebot—receives a blank HTML page. Then, JavaScript runs to generate the fully rendered HTML.
Google can render client-side, JavaScript-driven pages. But, it may delay rendering and indexing.
| Benefits of CSR | Drawbacks of CSR |
|---|---|
| Reduced server load | Slower initial load times |
| Enhanced interactivity | SEO challenges |
| Improved scalability | Increased complexity |
| Faster page transitions | Performance variability |
Dynamic Rendering
Dynamic rendering, or prerendering, is a hybrid approach.
Tools like Prerender.io detect Googlebot and other crawlers. They then send a fully rendered webpage from a cache.
This way, search engines don’t need to run JavaScript.
At the same time, regular users still get a CSR experience. JavaScript is executed and content is rendered on the client side.
Google says dynamic rendering isn’t cloaking. The content shown to Googlebot just needs to be the same as what users see.
However, it warns that dynamic rendering is a temporary solution. This is due to its complexity and resource needs.
| Benefits of Dynamic Rendering | Drawbacks of Dynamic Rendering |
|---|---|
| Better SEO | Complex setup |
| Crawler compatibility | Risk of cloaking |
| Optimized UX | Tool dependency |
| Scalable for large sites | Performance latency |
Which Rendering Approach is Right for You?
The right rendering approach depends on several factors.
Here are key considerations to help you determine the best solution for your website:
| Rendering Option | Best for | When to Choose | Requirements |
|---|---|---|---|
| Server-Side Rendering (SSR) | SEO-critical sites (e.g., ecommerce, blogs)
Sites relying on organic traffic Faster Core Web Vitals (e.g., LCP) |
Need timely indexing and visibility
Users expect fast, fully-rendered pages upon load |
Strong server infrastructure to handle higher load
Expertise in SSR frameworks (e.g., Next.js, Nuxt.js) |
| Client-Side Rendering (CSR) | Highly dynamic user interfaces (e.g., dashboards, web apps)
Content not dependent on organic traffic (e.g. behind login) |
SEO is not a top priority
Focus on reducing server load and scaling for large audiences |
JavaScript optimization to address performance issues
Ensuring crawlability with fallback content |
| Dynamic Rendering | JavaScript-heavy sites needing search engine access
Large-scale, dynamic content websites |
SSR is resource-intensive for the entire site
Need to balance bot crawling with user-focused interactivity |
Pre-rendering tool like Prerender.io
Bot detection and routing configuration Regular audits to avoid cloaking risks |
Knowing these technical solutions is important. But the best approach depends on how your website uses JavaScript.
Where does your site fit?
- Minimal JavaScript: Most content is in the HTML (e.g., WordPress sites). Just make sure search engines can see key text and links.
- Moderate JavaScript: Some elements load dynamically, like live chat, AJAX-based widgets, or interactive product filters. Use fallbacks or dynamic rendering to keep content crawlable.
- Heavy JavaScript: Your site depends on JavaScript to load most content, like SPAs built with React or Vue. To make sure Google can see it, you may need SSR or pre-rendering.
- Fully JavaScript-rendered: Everything from content to navigation relies on JavaScript (e.g., Next.js, Gatsby). You’ll need SSR or Static Site Generation (SSG), optimized hydration, and proper metadata handling to stay SEO-friendly.
The more JavaScript your site relies on, the more important it is to optimize for SEO.
JavaScript SEO Best Practices
So, your site looks great to users—but what about Google?
If search engines can’t properly crawl or render your JavaScript, your rankings could take a hit.
The good news? You can fix it.
Here’s how to make sure your JavaScript-powered site is fully optimized for search.
1. Ensure Crawlability
Avoid blocking JavaScript files in the robots.txt file to ensure Google can crawl them.
In the past, HTML-based websites often blocked JavaScript and CSS.
Now, crawling JavaScript files is crucial for accessing and rendering key content.
2. Choose the Optimal Rendering Method
It’s crucial to choose the right approach based on your site’s needs.
This decision may depend on your resources, user goals, and vision for your website. Remember:
- Server-side rendering: Ensures content is fully rendered and indexable upon page load. This improves visibility and user experience.
- Client-side rendering: Renders content on the client side, offering better interactivity for users
- Dynamic rendering: Sends crawlers pre-rendered HTML and users a CSR experience
3. Reduce JavaScript Resources
Reduce JavaScript size by removing unused or unnecessary code. Even unused code must be accessed and processed by Google.
Combine multiple JavaScript files to reduce the resources Googlebot needs to execute. This helps improve efficiency.
4. Defer Scripts Blocking Content
You can defer render-blocking JavaScript to speed up page loading.
Use the “defer” attribute to do this, as shown below:
