SPA

Single Page Application

A web app where the page never fully reloads — JavaScript swaps views, updates the URL, and re-renders content in place. Contrast with traditional multi-page sites where every link triggers a server round-trip.

When you'd see it: Most modern web apps — Gmail, Notion, Linear, Figma. Also many marketing and reference sites. Once the page loads, navigation between tabs or sections is instant because nothing reloads.

Why it matters: SPAs feel faster and more app-like than traditional sites, at the cost of more JavaScript and more complexity for SEO and accessibility. The pattern enables hash routing, client-side state, and offline-readable architectures.

Common mistakes: Building everything as an SPA when a simpler multi-page setup would serve the user better. SPAs fit when navigation needs to feel app-like; they're overhead when the site is mostly read-and-leave.

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