Google can execute JavaScript, but it does so in a second pass that is queued, delayed and occasionally skipped for low-value pages. Most other crawlers — including the ones behind AI answer engines — do not execute it at all. Content that only exists after hydration is therefore invisible to a growing share of the machines you care about.
The safe default in 2026 is to serve the main content, the metadata, the internal links and the structured data in the initial HTML, and to use client-side rendering for interactivity on top of that. Verify with the URL Inspection tool's rendered HTML and with a plain `curl` of the page: if the text is not in the source, treat it as absent.