store.ts

import * as React from "react";

/**
A hook to simply use state between components
Warning: this only works with function components (like any hook)

Usage:

// You can put this in an central file and import it too
const useStore = createStore({ count: 0 })

// And this is how you use it from any component
export function Example() {

    const [store, setStore] = useStore()
    const updateCount = () => setStore({ count: store.count + 1 })

    return <div onClick={updateCount}>{store.count}</div>
}
*/

export function createStore<T>(state: T) {
    // Store the initial state, copy the object if it's an object
    let storeState: T = typeof state === "object" ? { ...state } : state

    // Keep a list of all the listener, in the form of React hook setters
    const storeSetters = new Set<Function>()

    // Create a set function that updates all the listeners / setters
    const setStoreState = (state: Partial<T>) => {
        // If the state is an object, make sure we copy it
        storeState =
            typeof state === "object" ? { ...storeState, ...state } : state
        // Update all the listeners / setters with the new value
        storeSetters.forEach((setter) => setter(storeState))
    }

    // Create the actual hook based on everything above
    function useStore(): [T, typeof setStoreState] {
        // Create the hook we are going to use as a listener
        const [state, setState] = React.useState(storeState)
        // If we unmount the component using this hook, we need to remove the listener
        React.useEffect(() => () => storeSetters.delete(setState), [])
        // But right now, we need to add the listener
        storeSetters.add(setState)
        // Return the state and a function to update the central store
        return [state, setStoreState]
    }

    return useStore
}

It seems like TypeScript got a bit stricter with warnings, but it should totally work.

Great, got it working indeed. What would be the right way to get this working on a class?

EDIT: nvm, figured out it was preferably to convert old class to a function. got it working now.