Rendering is a delivery decision
JavaScript is not inherently bad for SEO. Problems appear when important content, links or metadata depend on an unreliable client-side path, when server and client output diverge, or when an application creates URLs and states search engines cannot interpret cleanly.
Inspect the HTML that arrives
Check the raw response, the rendered DOM and the visible interface. Primary content, canonical tags, headings, status codes and internal links should not rely on a user interaction or an API response that search engines may not receive consistently.
Hydration and parity
Hydration errors can replace, hide or alter server-rendered content. Monitor the browser console, test without JavaScript where useful and compare key templates at scale. A page can look correct to a developer while sending conflicting signals during rendering.
Routing and internal links
Client-side navigation should still expose crawlable anchor elements and stable URLs. Filters, infinite scroll and modal states need explicit decisions about which states deserve URLs, which should be linked and how duplicate combinations are controlled.
Measure the release
Test representative templates before production, confirm status and metadata at the edge, inspect rendered output, re-crawl after release and use Search Console to see how Google processes the change. Verification belongs inside the release plan.
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