votes.js

function reducer(state, action) {
  switch (action.type) {
    case UPDATE_VOTES:
      const updateVotesList = state.polls.map((poll, ind) => {
        if (ind === action.question) {
          return poll.answers.map((ans, index) => 
            index === action.index
              ? { ...ans, votes: ans.votes + action.votes }
              : ans;
          );
        } else {
          return { polls: { ...state.polls } };
        }
      });
      return {
        ...state,
        polls: updateVotesList,
      };
    default:
      return state;
}

case UPDATE_VOTES:
      const updateVotesList = state.polls.map((poll, ind) => {
        if (ind === action.question) {
          return {
            ...poll,
            answers: poll.answers.map((ans, index) => {
              if (index === action.index) {
                return { ...ans, votes: ans.votes + action.votes };
              }
              return ans;
            }),
          };
        }
        return poll;
      });
      return {
        ...state,
        polls: updateVotesList,
      };

case UPDATE_VOTES:
      return state.polls.map((poll, ind) => (
        ind !== action.question
          ? poll
          : {
            ...poll,
            answers: poll.answers.map((ans, index) => (
              index !== action.index
                ? ans
                : { ...ans, votes: ans.votes + action.votes }
            )
          }
      );