My withLocalState combinator, soon to be published seperately

withLocalState.ts

type SimpleMerge<Global, Local> = { global: Global, local: Local };
interface Merger<Global, Local, T> {
    merge(g: Global, l: Local): T;
    extract(t: T): SimpleMerge<Partial<Global>, Partial<Local>>;
}

function withLocalState<Global, Local, T = SimpleMerge<Global, Local>>(component: Component<T>, merger?: Merger<Global, Local, T>, stateChannel = 'state', localChannel = '_localState'): Component<Global> {
    const defaultMerger: Merger<Global, Local, SimpleMerge<Global, Local>> = {
        merge: (global, local) => ({ global, local }),
        extract: identity
    };

    const wrapper = function WithLocalState(sources: any) {
        const m = merger ? merger : defaultMerger;
        const state$ = xs.combine<Global, Local>(sources[stateChannel].stream, sources[localChannel].stream.startWith(undefined))
            .map(([g, l]) => m.merge(g, l))
            .remember();

        const sourcesCopy = { ...sources };
        delete sourcesCopy[localChannel];

        const sinks: any = component({ ...sourcesCopy, [stateChannel]: new StateSource<T>(state$, 'withLocalState') });

        const updated$ = !sinks[stateChannel] ? xs.never() :
            sinks[stateChannel]
                .compose(sampleCombine<any>(state$))
                .map(([fn, x]: any) => m.extract(fn(x)));
        const global$ = updated$.map((s: any) => (state: Global) => ({ ...state, ...s.global }));
        const local$ = updated$.map((s: any) => (state: Local) => ({ ...state, ...s.local }));

        return {
            ...sinks,
            [stateChannel]: global$,
            [localChannel]: local$
        };
    };

    return withState(wrapper as any, localChannel) as any;
}

const customMerger: Merger<MainState, LocalState, State> = {
    merge: (g, l) => ({ ...l, authToken: g.authToken }),
    extract: t => ({ global: { authToken: t.authToken }, local: omit(['authToken'], t) })
};

export const Login = withLocalState<MainState, LocalState, State>(LoginComponent, customMerger);