Why it matters to a buyer
A site built entirely in client-side JavaScript can look perfect in a browser and still be crawled as a near-blank page, because Googlebot has to run a second, more expensive rendering pass to see what a normal browser sees instantly, and that pass is queued rather than immediate. For a buyer evaluating a framework or a rebuild, this is a real risk to weigh against the developer experience benefits, particularly for a content-heavy or ecommerce site that depends on organic search.
How it is measured or applied
The safest approach for search-dependent content is to serve meaningful HTML on first response, through server-side rendering, static generation, or hydration frameworks that do this by default, rather than relying on the crawler to execute client-side JavaScript correctly. Where client-side rendering is unavoidable, critical content and links should not depend on user interaction to appear. It is diagnosed by comparing a page's raw HTML response against its fully rendered DOM, and by using Search Console's URL inspection tool, which shows the rendered HTML Google actually used to index the page.
Sources
- JavaScript SEO basics, Google Search Central
