file.ts

/**
 * Maps selector objects with keys
 * 
 * @param   { SelectorsMapObject } selectorsMapObject selectors map object
 * @returns { SelectorsObject } selectors object
 */
export function combineSelectors<S extends SelectorsMapObject, K extends keyof S>(selectorsMapObject: S): S[K] {
    const combinedSelectors = {};

    Object.keys(selectorsMapObject).forEach(key => {
        if (process.env.NODE_ENV !== 'production') {
			if (typeof selectorsMapObject[key] === 'undefined')
				warning(`No selector or selectorsObject provided for key "${ key }"`);
        }

        if (typeof selectorsMapObject[key] === 'object') {
            const storeKey = key;

            Object.keys(selectorsMapObject[storeKey]).forEach(selectorKey => {
                if (process.env.NODE_ENV !== 'production') {
                    if (typeof selectorsMapObject[storeKey][selectorKey] === 'undefined')
                        warning(`No selector provided for key "${ selectorKey }"`);
                    else if (typeof selectorsMapObject[storeKey][selectorKey] !== 'function')
                        warning(`No selector provided for key "${ selectorKey }"`);
                }

                if (typeof selectorsMapObject[storeKey][selectorKey] === 'function')
                    combinedSelectors[selectorKey] = (state, ...args) =>
                        selectorsMapObject[key][selectorKey](state[storeKey], ...args);
            });
        }
    });

    return combinedSelectors as S[K];
}