createGlobalState

createGlobalState(initialValue) returns a hook that behaves like useState, except every component calling it shares one value. You call the factory once at module scope; the value it holds lives in a closure, outside React, and any component can read it and write it without a prop or a provider in sight.

That last part is the whole problem. React re-renders in response to its own state setters. A variable in a module closure can change a thousand times and nothing on screen moves, because nothing told React. So a store outside React needs three things wired by hand: a way to read the current value, a way to subscribe to changes, and a way to tell React that a subscribed component is now out of date.

This is the smallest question in the catalog that has all three. No selectors, no reducers, no atoms — one value, shared.

Signature

function createGlobalState<S>(initialValue: S): () => [
  S,
  (next: S | ((prev: S) => S)) => void,
];

Examples

Call the factory once, at module scope, and export the hook:

// store.js
const useCount = createGlobalState(0);

Then any component uses it like useState — with no provider and no props:

function Counter() {
  const [count, setCount] = useCount();
  return <button onClick={() => setCount((n) => n + 1)}>{count}</button>;
}

// A sibling. Nothing connects it to Counter.
function Badge() {
  const [count] = useCount();
  return <span>{count}</span>; // clicking the button moves this
}

Notes

• One store per call. Two createGlobalState calls are two independent values. The factory is the store; the hook is a window onto it.
• useState's contract. setValue takes a value or an updater (prev) => next, and its identity is stable, so it is safe in a dependency array.
• The store is not component state. It outlives every subscriber. Unmount the whole tree, mount a fresh component, and the value is still whatever it was.
• Mounting late is normal. A component that first renders after the value has moved must show the current value, not the initial one.
• Unmounting unsubscribes. A component that has left must not be updated, and must not keep the store from collecting it.
• Out of scope — selectors, equality functions, reducers, and persistence. One value, read and written whole.