Build a Mini UI Framework - The Magic, Demystified

Build the machinery inside React, Vue, and Svelte yourself in ~120 lines of plain JavaScript: a proxy-based reactivity system, effects and computed values, a virtual DOM, and a diff.

1. Reactive Objects Build the atom of reactivity: a JavaScript Proxy that intercepts every property read and write, so your data can announce its own changes.
2. Effects and Computed Automate dependency tracking with one global variable: while an effect runs, every property it reads subscribes it - the trick behind Vue's templates, Svelte's effects, and Angular's signals.
3. The Virtual DOM Represent UI as cheap description objects with an h() function, and write a renderer that turns a tree of them into HTML - React's core idea, built in 30 lines.
4. The Diff Compare two vnode trees and emit the minimal patch list - then break positional matching with a reordered list and fix it with keys, finally seeing why every framework demands them.
5. Wiring It Together Connect reactivity to rendering: an effect re-describes the UI on every state change and the diff reports the minimal patches - one working micro-framework, then the map to React, Vue, Svelte, and Angular.