01
Write a minimal observable store in plain JavaScript.
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A store holds state and notifies subscribers:
function createStore(initial) {
let state = initial;
const listeners = new Set();
return {
get: () => state,
set(update) {
state = { ...state, ...update };
listeners.forEach(fn => fn(state));
},
subscribe(fn) {
listeners.add(fn);
return () => listeners.delete(fn);
}
};
}
const cart = createStore({ items: 0 });
const stop = cart.subscribe(s => (badge.textContent = s.items));
cart.set({ items: 2 });
The returned unsubscribe function prevents memory leaks.