A single-page application loads once, then rewrites the screen in place as the user navigates — no full page reloads. The result feels like desktop software: instant transitions, persistent state. The cost is that the raw page is nearly empty until JavaScript runs, which search engines tolerate and most AI crawlers do not.
The fix is prerendering or server-side rendering: real HTML for every URL, the app for every human. How we do it for React sites is in technical SEO for React.