Single-page application

A single-page application loads once and then rewrites its own content as the user navigates, fetching data in the background instead of asking the server for a whole new page each time. Every web application that feels like desktop software — a dashboard, an editor, a mail client — works this way.

The gain is responsiveness after the first load: moving between screens costs one small data request rather than a full page render. The cost is that the first load is heavier, because the browser must download and run the application before anything appears.

That cost is why a marketing site built as a single-page application is usually a mistake. A visitor who arrives from a search result wants the text immediately, not after a JavaScript bundle has finished parsing — which is the problem server-side rendering and static site generation exist to solve.