createReducer.js

export function createReducer(initialState, handlers) {
  const match = (key, type) => (
    key
      .replace(/ /g, '')
      .split(',')
      .reduce((acc, k) => (
        acc || type.indexOf(k) > -1 ? k : null
      ), null)
  );

  const matchKey = (keys, type) => (
    keys.indexOf(type) > -1 && type
      || keys.reduce((acc, key) => (
        key.indexOf(",") > -1 && match(key, type) || acc
      ), null)
    || (keys.indexOf("_") > -1 && "_") || ""
  );

  return function reducer(state = initialState, action) {
    const matchedKey = matchKey(Object.keys(handlers), action.type);
    return handlers.hasOwnProperty(matchedKey) ? handlers[matchedKey](state, action) : state;
  };
}