Lesson 26 — Ultimate: reactive store

Boss level: a store that announces changes

A store holds the app's state in one place. You never change state directly; you dispatch an action (a message like "inc"), a reducer function computes the new state from the old state and the action, and every subscriber is told about the new state. This is the idea behind Redux and Vue's reactivity.

const counter = (s, a) => (a === "inc" ? s + 1 : s);
counter(0, "inc");   // 1 — the reducer only computes, it never stores

Why it matters: one predictable path for every change makes big UIs debuggable.