JavaScript rendering issues arise when web content generated or modified by JavaScript code is not properly rendered or indexed by search engines. JavaScript is commonly used for dynamic content, interactive features, and single-page applications (SPAs) that rely on client-side rendering. Search engines like Google can render and execute JavaScript to index web content, but they may encounter challenges with JavaScript-heavy websites due to rendering delays, execution errors, or content obfuscation. Webmasters should optimize JavaScript code, use server-side rendering (SSR) or pre-rendering techniques, and provide fallback content for non-JavaScript users to ensure search engine compatibility and indexing. To address JavaScript rendering issues, webmasters should use Google's Fetch as Google tool to render and index JavaScript-generated content, test website performance and rendering with tools like Lighthouse or PageSpeed Insights, and follow Google's JavaScript SEO best practices and recommendations for improved search engine visibility. They can also monitor search appearance and index coverage in Google Search Console for JavaScript-rendered content and crawl errors.