Heavy frameworks inflate bundles and delay interactivity while many dynamic UIs need only disciplined DOM work. This deep dive reframes the bloat problem, walks through core DOM APIs and mutation strategies, shows event delegation and measurable KPIs, exposes common pitfalls, and proves real gains via a React-to-vanilla migration with 45% smaller bundles, 30% faster first contentful paint, and 20% lower memory usage. Learn repeatable patterns you can ship today without the framework payload.