JavaScript-heavy websites often face significant SEO challenges that traditional audits miss. Search engines can struggle to render and index JavaScript-generated content, leading to invisible pages, missing metadata, and broken internal links. This workflow systematically identifies rendering issues, content accessibility problems, and performance bottlenecks that prevent JavaScript sites from ranking effectively.
You'll emerge with a prioritized list of JavaScript SEO issues, evidence of what search engines actually see versus what users see, and actionable recommendations for fixing client-side rendering problems that block organic visibility.
What You'll Need
A JavaScript-heavy website to audit, Screaming Frog SEO Spider (paid version for JavaScript rendering), Google Search Console access for the target site, and Chrome browser for manual testing. You should understand the difference between client-side and server-side rendering, plus basic familiarity with how search engine crawlers process JavaScript.
Step 1: Configure Screaming Frog for JavaScript Rendering
Time: 15 minutes | Tool: Screaming Frog Open Screaming Frog and navigate to Configuration > Spider > Rendering. Enable "JavaScript Rendering" and set the rendering wait time to 5 seconds minimum - many JavaScript frameworks need this buffer to fully execute. Under Configuration > Spider > Advanced, increase the crawl delay to 2 seconds to avoid overwhelming the server during JavaScript processing. Configure the JavaScript settings to render like Googlebot by setting the User Agent to "Googlebot" under Configuration > User Agent > Custom. This ensures you're seeing what Google's crawler actually encounters when processing your JavaScript content. Pro tip: For React or Vue applications with heavy AJAX loading, increase the rendering wait time to 10 seconds for the initial crawl to capture dynamically loaded content.
Step 2: Perform Dual Crawls (With and Without JavaScript)
Time: 30-45 minutes | Tool: Screaming Frog Run two separate crawls of your website. First, crawl with JavaScript rendering enabled to see what search engines should ideally index. Save this crawl data as "JS-Enabled-Crawl." Then disable JavaScript rendering in Configuration > Spider > Rendering and run a second crawl, saving it as "JS-Disabled-Crawl." The JavaScript-disabled crawl shows what older search engines or crawlers with JavaScript issues would see. Compare the total page count, response codes, and discovered URLs between both crawls. Pages that only appear in the JavaScript-enabled crawl indicate content that requires JavaScript to be accessible. Export both crawls' Internal HTML pages to CSV files. You'll use these to identify discrepancies in content accessibility, title tags, meta descriptions, and internal link structures that only appear after JavaScript execution.
Step 3: Analyze Content Accessibility Gaps
Time: 25 minutes | Tool: Screaming Frog + Manual Analysis Compare the page counts from both crawls in the Internal tab. If your JavaScript-disabled crawl shows significantly fewer pages, you have content accessibility issues. Focus on pages with "200" status codes in the JavaScript-enabled crawl that returned "404" or weren't discovered in the JavaScript-disabled crawl. Check the Title and Meta Description tabs in both crawls. Pages showing empty or generic titles/descriptions in the JavaScript-disabled crawl but populated ones in the JavaScript-enabled crawl indicate metadata that's dynamically generated client-side. These pages risk having poor snippet optimization since search engines might not consistently render the JavaScript. Review the Images tab to identify images that only appear after JavaScript execution. Alt text that's added via JavaScript might not be accessible to search engines, creating missed optimization opportunities for image SEO.
Step 4: Examine Google Search Console Indexing Data
Time: 20 minutes | Tool: Google Search Console Navigate to Google Search Console's Coverage report under Index > Coverage (or Page Indexing in newer interface). Look for URLs marked as "Discovered - currently not indexed" or "Crawled - currently not indexed" that match pages from your JavaScript-enabled crawl. This suggests Google is finding these URLs but struggling to process their JavaScript content. Check the Page Experience report for Core Web Vitals issues. JavaScript-heavy sites often have poor Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS) scores due to render-blocking JavaScript. Poor Core Web Vitals can indirectly impact SEO performance. Use the URL Inspection tool to test 5-10 critical pages from your JavaScript-enabled crawl. Pay attention to the "HTML" section in the inspection results - this shows exactly what Googlebot rendered. Compare this to what users see in their browsers to identify content that's missing from Google's rendered version.
Step 5: Test Page Speed Impact of JavaScript
Time: 20 minutes | Tool: PageSpeed Insights Test your homepage and 3-5 key landing pages in PageSpeed Insights, focusing on the mobile scores. JavaScript often causes significant mobile performance issues due to slower processing on mobile devices. Look for "Reduce unused JavaScript" and "Remove render-blocking resources" recommendations in the Opportunities section. Check the Diagnostics section for "Avoid enormous network payloads" warnings. JavaScript frameworks can create large bundle sizes that slow initial page rendering. Note any "Avoid non-composited animations" issues, which often stem from JavaScript-driven animations that bypass the GPU. Document the First Contentful Paint (FCP) and Largest Contentful Paint (LCP) metrics for each tested page. JavaScript sites should target LCP under 2.5 seconds, but many exceed 4+ seconds due to render delays. Pro tip: Test the same pages with JavaScript disabled using Chrome DevTools (F12 > Settings > Debugger > Disable JavaScript) to see the performance difference and identify how much JavaScript impacts loading speed.
Step 6: Create JavaScript SEO Action Plan
Time: 15 minutes | Tool: Manual Analysis Compile your findings into prioritized recommendations. High-priority issues include pages only accessible via JavaScript, critical metadata missing in non-JavaScript crawls, and Core Web Vitals failures. Medium-priority items cover internal linking issues and image optimization problems discovered in your crawl comparison. Create specific implementation recommendations: suggest server-side rendering (SSR) or static site generation (SSG) for content-heavy pages, recommend preloading critical JavaScript resources, and identify opportunities to move essential content above JavaScript dependency layers. Document which pages need immediate attention based on their organic traffic potential and current indexing status in Search Console. Focus first on high-traffic pages that show significant discrepancies between JavaScript-enabled and disabled crawls.
Common Pitfalls
- Running JavaScript crawls too quickly without sufficient rendering wait time, missing dynamically loaded content that loads after initial page render
- Comparing crawls from different time periods when site content may have changed, leading to false positives in accessibility gap analysis
- Testing only desktop performance in PageSpeed Insights while ignoring mobile JavaScript rendering issues that affect mobile-first indexing
- Focusing only on technical rendering without checking if the rendered content actually matches user-visible content in real browsers
Expected Results
You'll have a comprehensive view of how search engines process your JavaScript site versus what users experience. Expect to find 15-30% of content accessibility issues on heavily JavaScript-dependent sites, plus specific Core Web Vitals improvement opportunities worth 10-20 point PageSpeed score increases. Most audits reveal 3-5 critical pages requiring immediate server-side rendering implementation and 10-15 pages needing JavaScript optimization for better search engine compatibility.