Vite vs Bundler — Dev Server Startup

A bundler must crawl and build your whole app before the dev server is ready. Vite serves source over native ESM and only transforms what the browser actually requests. Drag the project size and race them.

Project size: 200 modules

Bundler (eager)0 ms

idle

Builds the entire dependency graph up front — startup scales with project size.

Vite (native ESM)0 ms

idle

Pre-bundles deps once, then serves source on demand — startup stays nearly flat.

Why the gap

Concern	Bundler	Vite
Dev startup	build everything first	serve on demand
Scales with app size?	yes (linear)	mostly no
What runs your code	bundle	the browser (native ESM)
Production build	bundler	Rolldown (Vite 8)
HMR speed	often whole-graph	single module

Vite still bundles for production — unbundled ESM means too many requests for the real web. Dev and prod use different strategies on purpose.