Single Page Application (SPA).

On a classic website, every click on a link loads a new HTML page from the server. A single page application works differently: the browser loads an almost empty HTML shell and a larger JavaScript bundle once. After that the framework, such as React, Vue or Angular, takes over. It fetches data through interfaces, builds the views in the browser and changes the URL in the address bar without reloading the page. For the user it feels as smooth as an installed app.

The strengths lie in applications with a lot of interaction: dashboards, client portals, booking systems, admin interfaces, tools that people use for long stretches at a time. What matters there is that switching between views happens instantly and that states such as filters or inputs are preserved. Many web apps and progressive web apps are therefore built entirely or partly as SPAs.

The weaknesses show on public websites. Because the content is only created in the browser, a crawler initially sees just the empty shell. Google can render JavaScript, but it does so in a second step, with a delay and not always completely; many AI crawlers do not execute JavaScript at all and see nothing. Typical errors add to this: missing or identical title tags, soft 404s because the server returns status 200 for every URL, and internal links that exist only as click handlers rather than real links. JavaScript SEO describes these problems in detail.

The first load suffers too: before anything meaningful appears, the JavaScript has to be loaded and executed, which shows in the Largest Contentful Paint. Modern frameworks solve this by rendering the first view on the server and then continuing in the browser like an SPA. Next.js, for example, delivers finished HTML and still switches between pages without a full reload. For websites that are meant to be found, this is usually the better choice than a pure SPA.